SPMM.S1.0223.06 Compressors Manual PDF

ADNOC Classification: Internal THE CONTENTS OF THIS DOCUMENT ARE [PROPRIETARY AND CONFIDENTIAL] Specialization Mechanical SPMM.S1.0223.06 Compressors VERSION: 0.1 DOCUMENT OWNER: Academic Services ADNOC Classification: Internal INTENDED LEANING OUTCOMES On completion of this module, the candidates will be able to: 1. Outline the function and operation of air compressors Performance Criteria: 1.1 Describe the function and operating principles of air compressors in the oil and gas industry 1.2 Classify the different types of air compressors. 1.3 Identify the main components & principles of construction of air compressors 1.4 Identify the main differences between reciprocating air compressors and rotary air compressors 1.5 Describe the normal operating parameters and tolerances for air compressors 1.6 Identify the different seal types for wet seal oil systems & dry gas seals 2. Outline typical signs of fault, damage, wear, and corrosion in air compressors Performance Criteria: 2.1. Identify the typical electrical and mechanical faults which can occur for air compressors 2.2. Identify the common signs of damage, wear and corrosion which can occur for air compressors 2.3. Identify the typical planned and preventative maintenance for air compressors. 2.4. Identify the typical maintenance techniques/ procedures/ routines for air compressors. 3. Describe typical routine maintenance requirements of air compressors Performance Criteria: 3.1. Identify the content and use of technical guidelines of air compressors 3.2. Identify the maintenance routines / schedules determined by the company / air compressors manufacturer. 3.3. Identify the content of air compressors manufacturers’ technical specifications/manual 3.4. Identify the maintenance checklists, work methods of air compressors 3.5. Identify the conventions, symbols, legends, and abbreviations used for air compressors SPMM.S1.0223.06 Compressors Version: 0.1 2 ADNOC Classification: Internal TABLE OF CONTENTS Paragraph Page 1. EQUIPMENT – AIR COMPRESSORS..............................................................................................4 1.1 FUNCTION AND OPERATING PRINCIPLES OF AIR COMPRESSORS IN THE OIL AND GAS INDUSTRY......................................................................................................................4 1.2 MAIN COMPONENTS & PRINCIPLES OF CONSTRUCTION OF AIR COMPRESSORS..11 1.3 NORMAL OPERATING PARAMETERS & TOLERANCES FOR AIR COMPRESSORS...40 1.4 MAIN DIFFERENCES BETWEEN RECIPROCATING AIR COMPRESSORS AND ROTARY AIR COMPRESSORS...........................................................................................43 1.5 DIFFERENT SEAL TYPES FOR WET SEAL OIL SYSTEMS & DRY GAS SEALS...........45 2. ROUTINE MAINTENANCE TECHNIQUES FOR AIR COMPRESSORS.......................................49 2.1 TYPICAL ELECTRICAL & MECHANICAL FAULTS FOR AIR COMPRESSORS..............49 2.2 COMMON SIGNS OF DAMAGE, WEAR & CORROSION FOR AIR COMPRESSORS.....51 2.3 TYPICAL PLANNED & PREVENTATIVE MAINTENANCE FOR AIR COMPRESSORS....53 2.4 TYPICAL MAINTENANCE TECHNIQUES/ PROCEDURES/ ROUTINES FOR AIR COMPRESSORS...................................................................................................................57 3. TECHNICAL INFORMATION AND GUIDELINES..........................................................................59 3.1 CONTENT AND USE OF TECHNICAL GUIDELINES E.G. ENGINEERING /TECHNICAL DRAWINGS (SCHEMATICS/ ISOMETRICS), PLANT LAYOUTS.......................................59 3.2 MAINTENANCE ROUTINES/SCHEDULES DETERMINED BY COMPANY AND MANUFACTURER OF AIR COMPRESSORS......................................................................63 3.3 MANUFACTURERS’ TECHNICAL SPECIFICATIONS/MANUALS.....................................65 3.4 MAINTENANCE CHECKLISTS, WORK METHODS, COMMISSIONING CHECKLISTS...69 3.5 CONVENTIONS, SYMBOLS, LEGENDS AND ABBREVIATIONS USED FOR AIR COMPRESSORS...................................................................................................................75 SPMM.S1.0223.06 Compressors Version: 0.1 3 ADNOC Classification: Internal 1. EQUIPMENT – AIR COMPRESSORS 1.1 FUNCTION AND OPERATING PRINCIPLES OF AIR COMPRESSORS IN THE OIL AND GAS INDUSTRY 1.1.1. FUNCTION OF AIR COMPRESSORS Compressors are the prime movers of gas and air in oil and gas process industries. They are used to increase the inlet pressure of the gas and deliver it at the specified discharge pressure and flow rate in a process application. In oil and gas process industries compressors are available in a variety of types, models, and sizes, each of which fulfils a given need. An air compressor is a specific type of compressor provide pressurized air to operate tool or instrument air systems. Figure (1.1) Typical Compressed Air System An air compressor is a machine that takes in filtered air from the atmosphere and forces it into a smaller space. The compressor then sends the compressed air to a holding tank, called a receiver. The process of squeezing air into a smaller space (compression) raises the air’s pressure and adds energy to it. When this pressurized air is allowed to escape from the receiver, it releases its energy. This released energy can perform work. SPMM.S1.0223.06 Compressors Version: 0.1 4 ADNOC Classification: Internal 1.1.2. OPERATING PRINCIPLES OF AIR COMPRESSOR Compressors come in two basic types, according to their basic principles of operation. The two basic types are: ▪ Positive-displacement compressors ▪ Dynamic compressors Each type includes several different kinds of compressors as shown in the figure below. Figure (1.2) Compressors Classification POSITIVE DISPLACEMENT COMPRESSORS Compressors that operate by volumetric displacement are called a positive displacement compressor. PD compressors draw in and trap a volume of air in a chamber (cylinder or casing). They then reduce the volume of the chamber to compress the air, before discharged at high pressure. PD compressors operate either with reciprocating motion or rotary motion. Reciprocating Piston Compressors, Rotary Screw Compressors, sliding Vane Compressors, and lobe Compressors are all positive displacement compressors. This unit focused on the operation and maintenance of the common types of positive- displacement air compressors. SPMM.S1.0223.06 Compressors Version: 0.1 5 ADNOC Classification: Internal RECIPROCATING COMPRESSOR Reciprocating compressor or piston compressor is a positive-displacement compressor that uses pistons driven by a crankshaft to deliver a volume of gas/air at high pressure. Reciprocating compressors play a major role in the oil and gas, and petrochemical industry processes. They are designed to operate over a wide range of capacities and pressures: Small portable compressors may be adequate for the delivery of small volumes, at pressures of, say, 20 psi. Large industrial compressors may be required to deliver several million cubic feet per hour, at pressures approaching 15 000 psi. Small Portable Compressor Large industrial Compressor Figure (1.3) Examples for Reciprocating Compressor OPERATING PRINCIPLES OF RECIPROCATING COMPRESSOR In the reciprocating compressor, the compression cycle is composed of three phases: Suction, Compression, and Discharge. In a reciprocating piston compressor, a volume of gas is drawn into a cylinder, trapped, and compressed by piston and then discharged into the discharge line at high pressure. As the piston moves backwards/downwards it creates a low-pressure space inside the cylinder, allowing the outside air to flow through the valve and into the cylinder. Now, when the piston moves forward/upwards, the volume in the cylinder is reduced and the air is compressed. SPMM.S1.0223.06 Compressors Version: 0.1 6 ADNOC Classification: Internal Figure (1.4) Principle of Operation of Reciprocating Compressor The valves control the flow of the gas through the cylinder; these valves act as check valves. Valve springs, piston movement, and atmospheric pressure determine when the valves open and close. During the intake stroke, the downward movement of the piston creates a partial vacuum inside the cylinder. The spring-operated intake valve is forced open by the differential pressure between free air on one side and the partial vacuum inside the cylinder. As the valve opens, air fills the cylinder. The piston now moves into the compression stroke, forcing the intake valve closed and raising the pressure of the air trapped in the cylinder. When the pressure of this air is great enough to overcome the force of the spring-operated discharge valve, the valve opens, and the compressed air is discharged from the cylinder. CLASSIFICATION OF RECIPROCATING COMPRESSORS Not all reciprocating compressors look alike. They come in a variety of shapes, sizes, and capacities. However, reciprocating compressors are puts in categories, according to four factors: 1) number of cylinders 2) action (single-acting or double-acting) 3) number of stages (single-stage, multi-stage) 4) layout (the physical arrangement of the cylinders) The type and shape of a compressor depends on the space available, the positioning, and the air pressure required. SPMM.S1.0223.06 Compressors Version: 0.1 7 ADNOC Classification: Internal 1) CLASSIFICATION OF RECIPROCATING COMPRESSOR ACCORDING TO THE NUMBER OF CYLINDERS: Reciprocating compressors are single-cylinder (low capacity) or multiple-cylinder (higher capacity). Single-Cylinder Reciprocating Compressor Multiple-Cylinder Reciprocating Compressor Figure (1.5) Classification of Reciprocating Compressor According to the Number of Cylinders 2) CLASSIFICATION OF RECIPROCATING COMPRESSOR ACCORDING TO THE PISTON ACTION: A. SINGLE – ACTING COMPRESSOR Single acting reciprocating compressor handle the gas at one side of the piston and has one discharge per revolution of crankshaft. Single Acting Reciprocating Compressor Double Acting Reciprocating Compressor Figure (1.6) Classification of Reciprocating Compressor According to the Piston Action SPMM.S1.0223.06 Compressors Version: 0.1 8 ADNOC Classification: Internal A. DOUBLE – ACTING COMPRESSOR Double acting reciprocating compressor handle the gas at both sides of the piston and completes two discharge strokes per revolutions of crankshaft. Most heavy-duty compressors are double acting. 3) CLASSIFICATION OF RECIPROCATING COMPRESSOR ACCORDING TO THE NUMBER OF STAGES: Air compressors are available in single or multiple stages of compression. Single-stage compressors draw air from the atmosphere and discharge it into the receiver or storage tank. Two-stage compressors bring the air up to intermediate pressure in one cylinder and to final pressure in a second cylinder. Figure (1.7) Single-Stage and Two-Stage Reciprocating Compressor The first stage compresses air to an intermediate pressure, and then one or more additional stages compress it to the final discharge pressure. The discharge of air from one cylinder is piped to the suction line of another cylinder via the intercooler. The figure below shows a simple diagram of how a two-stage compressor operates. A two-stage compressor in principle consists of two single-stage compressors mounted in series upon a common crankshaft casing. Where two or more stages are employed, the unit is defined as a multistage air compressor. Multistage compressors produce higher discharge pressures. SPMM.S1.0223.06 Compressors Version: 0.1 9 ADNOC Classification: Internal Figure (1.8) Principle of Operation of Two-Stage Reciprocating Compressor ❖ INTERCOOLER The intercooler is a heat exchanger (air cooled or water cooled) that placed between the stages of the multi-stage compressor. E.g., in two stage compressors, the intercooler cools the compressed air coming from the first stage, before it enters the second stage. 4) CLASSIFICATION OF RECIPROCATING COMPRESSOR ACCORDING TO THE LAYOUT: The layout and orientation of the cylinder in reciprocating compressors determines whether the compressor is horizontal, vertical, V-shape, L-shape, or W-shape. Figure (1.9) Classification of Reciprocating Compressor According To the Layout SPMM.S1.0223.06 Compressors Version: 0.1 10 ADNOC Classification: Internal 1.2 MAIN COMPONENTS & PRINCIPLES OF CONSTRUCTION OF AIR COMPRESSORS 1.2.1. MAIN COMPONENTS AND PRINCIPLES OF CONSTRUCTION OF RECIPROCATING COMPRESSOR Reciprocating compressor parts can be divided into two main groups: Gas end. Power end. Figure (1.10) Single-Acting, Two-Stage, Vertical Reciprocating Compressor SPMM.S1.0223.06 Compressors Version: 0.1 11 ADNOC Classification: Internal Figure (1.11) Double-Acting, Single-Stage, Horizontal Reciprocating Compressor Figure (1.12) Two Stages Double Acting Horizontal Reciprocating Compressor SPMM.S1.0223.06 Compressors Version: 0.1 12 ADNOC Classification: Internal 1.2.1.1. GAS END The gas end is the group of parts that handle the gas/air in the compressors. Figure (1.13) Main Pats of Reciprocating Compressor Gas End A. CYLINDERS & LINERS The cylinders of industrial compressors are separable from the frame. They are attached to the frame by way of an intermediate part known as the distance piece. Normally most of the cylinders used in the process industries are equipped with replaceable liners. The purpose of the liner is to provide a renewable surface to the wearing portion of the cylinder. This saves the cost of replacing a complete cylinder once the bore has been worn or scored. A cylinder or liner usually wears at the points where the piston rings rub against it. Because of the weight of the piston, wear is usually greater at the bottom of a horizontal cylinder. To reduce the temperature during the compression cycle cylinders are equipped by means of water jacket or fins. The cylinder material is dependent on the diameter, pressure difference and the gas being handled by the compressor e.g.: ▪ Cast iron for the larger, low-pressure cylinders (The most common material) ▪ Steel for the smaller, high-pressure cylinders. SPMM.S1.0223.06 Compressors Version: 0.1 13 ADNOC Classification: Internal Cylinder without a liner nor cooling jacket Cylinder with a liner and cooling jacket Figure (1.14) Reciprocating Compressor Cylinder Types B. PISTON Piston is the heart of the reciprocating compressor; it transfers the energy from the crankcase (power end) to the gas in the cylinder. Compressor pistons are usually of three types: Solid single piece pistons made from cast iron or steel. These are used in small bore, high-pressure difference applications. Among the single piece type, hollow pistons are used for low-pressure difference and larger diameters. Figure (1.15) Compressor Piston Two-piece pistons can be made from either aluminum or cast iron. These are usually used where cylinder diameters are 10 inches and above. Reduced weight is one advantage of using aluminum as a material of construction. Two-piece designs aid in the installation of endless rider rings. Three-piece pistons are also used to aid the installation of endless rider rings. SPMM.S1.0223.06 Compressors Version: 0.1 14 ADNOC Classification: Internal C. PISTON RINGS Piston rings are sliding seals used to prevent or minimizes the leakage of compressed gas between piston and cylinder/liner. Another secondary function is to transfer the heat of the piston to the liner from where it can be exchanged with the cooling water in the jackets. Piston rings are made either in one piece with a gap or in several segments. Gaps in the rings allow them to move out and expand as the compressor reaches operating temperature. Figure (1.16) Piston Rings They are different types of rings material according to the compressor service: ▪ Lubricated service, metallic rings such as cast iron or bronze as well as non- metallic materials such as filled nylon are used. ▪ Non-lubricated service, the rings shall have good self-lubricated property such as PEEK (Polyether Ether Ketone) and other fluorocarbon compounds. In the case of horizontal cylinder piston, along with piston rings, an additional ring is used to reduce the wear between cylinder and piston and to bear the weight of the piston and the piston rod as it slides along the liner, it is called as wear band or Rider Ring. D. PISTON ROD The piston rod is fastened to the piston by means of special nut that is prevented from unscrewing. It transmits the reciprocating motion from the crosshead to the piston. The piston rod is normally made from alloy steel and must have a hardened and polished surface particularly where it passes through the cylinder packing. SPMM.S1.0223.06 Compressors Version: 0.1 15 ADNOC Classification: Internal Figure (1.17) Piston Rod Piston rod loading must be kept within the limits set by the compressor vendor because overloading can cause excess run-out of the rod resulting in premature packing wear. This, in turn, leads to leakage, reduced efficiency, and increased maintenance expense. E. PISTON ROD PACKING Piston rod packing prevents compressed gas from leaking along the piston rod. In compressors that operate below atmospheric pressure, rod packing prevents air from being drawn into the cylinder. Packing rings are made in segments for installation over the rod and to allow free radial movement down against the rod. Free radial movement allows for slight size variations and provides a means to accommodate ring wear. All types of packing rings are manufactured with an initial "end clearance" of sufficient size so that no adjustment is required throughout their useful life. The common types of rods packing rings are: ▪ Radial Ring or Pressure Breaker Ring ▪ Tangent Ring ▪ Backup ring Figure (1.18) Types pf Piston Rod Packing SPMM.S1.0223.06 Compressors Version: 0.1 16 ADNOC Classification: Internal The rings segments are held together by a spring installed in the groove running around the outside of the ring. A typical piston rod packing consists of series of cups each containing several seal rings side by side. The entire set of cups is held inside a stuffing box. Stuffing boxes can be lubricated, or non-lubricated, water-cooled and non-water cooled. Depend on the type of stuffing box; there are inside channels for cooling, gas recovery and lubrication of the piston rod packing. Figure (1.19) Stuffing Box The number of packing rings and type of system changes according to the cylinder maximum operating pressures. It is important to remember that the packing does not give an absolute seal. It only minimizes leakage from the cylinder. F. CYLINDER HEAD The small capacity compressors are equipped with removable cylinder head, which bolted to the top of the cylinder. The cylinder head houses the suction and discharge valves, and the capacity control device. SPMM.S1.0223.06 Compressors Version: 0.1 17 ADNOC Classification: Internal In most of the large capacity compressors the cylinder will accommodate the suction and discharge valves, and the capacity control device rather than the head. In this case the cylinder head cover the end of the cylinder. Cylinder Head of large capacity compressor Cylinder Head of small capacity compressor Figure (1.20) Cylinder Head of Reciprocating Compressor G. VALVES Compressor valves act as a non-return valve. The suction valve allows air to enter but not leave the compression cylinder. The discharge valve allows compressed air to pass into the discharge line (but not return to the cylinder), go through the cooler, and on to the receiver. There is no significant difference between suction and discharge valves, both operate in a similar manner, but in reverse directions. There are several different kinds of compressor valves: plate valves, ring valves, channel valves, feather valves, poppet valves, reed and concentric valves, to name just a few. Each design has specific criteria about the sealing element and all the other components are designed. The figure below shows the three common types of valves used in reciprocating compressors. Figure (1.21) Common Types Reciprocating Compressor Valves SPMM.S1.0223.06 Compressors Version: 0.1 18 ADNOC Classification: Internal Most valves essentially comprise of the following five components: ▪ Seat - They resist the differential gas pressure and wear on the surfaces in contact with valve sealing elements ▪ Guard (guard, stop plate, buffer, plate, etc.) – They have the following functions: o Provide a guide for the motion of the valve sealing element o Control the lift of the valve o Retains the valve return spring ▪ Sealing element (valve plate or valve ring, channel, poppet, feather strip, reed) – These open and close on rapidly alternating differential pressures and allow the gas to flow through them and then prevent the backflow of gas when the pressure reverses. ▪ Damping element (coil springs, cushion plates, spring plates, damping plates) – As the sealing elements open and close rapidly during every stroke, their stops against the seat and guard need to be cushioned to prevent early failures due to higher impacts. This cushioning is provided by the damping elements. ▪ Assembly element (bolts, nuts, retainer ring) – These are used to clamp all the component of the valve as one assembly. Figure (1.22) Exploded view for Metallic and Non-Metallic Plate Valve SPMM.S1.0223.06 Compressors Version: 0.1 19 ADNOC Classification: Internal 1.2.1.2. POWER END The parts of reciprocating compressor that assist in transferring power and converting rotary motion into reciprocating motion are grouped in this category. Figure (1.23) Main Pats Reciprocating Compressor Power End A. CRANKCASE The crankcase sometimes also called frame. The crankcase houses and supports the rotating parts, including the crankshaft and the connecting rods. It also houses the compressor’s main bearings, and it acts as the compressor’s lubrication oil reservoir. The crankcase is provided with easily removable covers for inspection and maintenance purposes, either on the top or on the side depending on the orientation of the compressor. In case of forced-lubrication system compressors, an oil pump is bolted to the crankcase and coupled to the crankshaft by a small coupling. The oil pump supplies lubricating oil to the main bearings, big-end bearing and small-end bearing, and guide piston. SPMM.S1.0223.06 Compressors Version: 0.1 20 ADNOC Classification: Internal Figure (1.24) Crankcase Assembly B. CRANKSHAFT The main purpose of the crankshaft is to convert rotary motion supplied by the driver into reciprocating motion via the connecting rods and crosshead. Normally the crankshaft is built in a single piece. When force lubrication is used, the crankshaft oil passages should be drilled through the shaft for distribution of lube oil. Figure (1.25) Crankshaft SPMM.S1.0223.06 Compressors Version: 0.1 21 ADNOC Classification: Internal The crankshaft ends are equipped with bearings called main bearings. ▪ Small capacity compressors normally used antifriction bearing (trapper roller bearings). ▪ Large capacity compressors normally used plain bearing (bush type or split type). Figure (1.26) Crankshaft Main Bearings C. CONNECTING RODS The connection rod is used to connect the crankshaft and the crosshead. The connecting rod normally has two plain bearings: ▪ Big end bearing is split type for installation purposes (crank shaft side). ▪ Small end bearing bush type (piston or crosshead side). Figure (1.27) Connecting Rod Like Crankshafts, the connecting rod should have drilled hole for oil passage between the big end bearing and small end bearing. SPMM.S1.0223.06 Compressors Version: 0.1 22 ADNOC Classification: Internal D. CROSSHEAD All industrial reciprocating compressors are equipped with a crosshead (also called guide piston). The crosshead is used to join piston rod with the connecting rod and to guide the piston rod in the cylinder bore. The following are the advantage of crosshead: ▪ The compressor can use a narrow piston, due to the use of narrow piston larger valve area for greater efficiency. ▪ Permits a longer stroke and greater capacity. ▪ Separates crankcase from the cylinder, allowing control of oil carryover into the cylinder. ▪ Gives greater stability to piston, eliminating piston “slap” and reducing ring wear ▪ Permits stronger piston design and higher operating pressures. Figure (1.28) Crosshead The crosshead is equipped with shoes which permit it to slide back and forth within the crosshead guide (also called guide cylinder). The shoes have channels for the distribution of lube oil. Connection between connecting rod and crosshead is realized by means of crosshead pin (also called gudgeon pin). The piston rod is connected to the crosshead by nut. SPMM.S1.0223.06 Compressors Version: 0.1 23 ADNOC Classification: Internal E. OIL WIPER RING Most reciprocating compressors use oil wiper rings to prevent crankcase oil from passing into the cylinder by scraping away the excess oil generated along the piston rod by its back and forwards movements. Also, in some instances oil wiper rings use to prevent condensate or cylinder and packing lubricant from entering the crankcase. Figure (1.29) Oil Wiper Rings F. Distance piece: Most industrial reciprocating compressors are equipped with a distance piece to separate the Gas end from Power End. It is provided with drain and vent arrangement and if required continuously purge with buffer gas. SPMM.S1.0223.06 Compressors Version: 0.1 24 ADNOC Classification: Internal 1.2.1.3. LUBRICATION IN RECIPROCATING COMPRESSORS The lubrication in the air compressors power end is a must, but the air compressors gas end is available as dry/oil-free and lubricated. In general, oil free compressors gas end is preferable in clean air applications such as instrumentation and controls services. Lubricated compressors gas end for utility air services are acceptable if a proper coalescing filtration system is included. The lubricating oil forms a surface film which reduces friction and, therefore, wear between the moving compressor parts. The lubricant also has a cooling function. Some of the heat generated by friction is carried away by the lubricating oil. Generally, two types of lubrication systems are uses to lubricate the reciprocating compressors: I. SPLASH LUBRICATION SYSTEM Splash lubrication is used in the small capacity compressors. Splash lubrication systems distribute lubricating oil by the splashing of the crank through the lubricant surface in the compressor crankcase. Splashing scoop (Dippers) may be attached to the crankshaft or connecting rod to enhance the oil splashing. Figure (1.30) Splash Oil System The two main advantages of splash systems are: ▪ Low initial cost ▪ Minimal operator attendance The main disadvantages are that splash systems are limited to: ▪ Small frame sizes ▪ The oil cannot be filtered SPMM.S1.0223.06 Compressors Version: 0.1 25 ADNOC Classification: Internal II. FORCED FEED LUBRICATION SYSTEM Forced feed lubrication system is the most common form of lubrication in industrial compressors. The forced feed lubrication system supplies filtered oil at the required pressure and temperature to the compressor parts. When forced feed lubrication is used in small capacity compressors, the pressure is supplied by means of an oil pump bolted to the crankcase and coupled to the crankshaft by a small coupling. Figure (1.31) Small Compressors Forced feed lubrication System In large capacity compressor the pressure is supplied by means of an electric motor driven pump. A standby pump is usually provided in order to achieve uninterrupted operation. The lubricating oil is collected and stored in the crankcase sump. The sump is equipped with a heater, level sight glass, coarse strainer and a drain. Oil from the crankcase sump first passes through the coarse strainer. This strainer is removable so that it can be cleaned. SPMM.S1.0223.06 Compressors Version: 0.1 26 ADNOC Classification: Internal Figure (1.32) Large Compressors Forced feed lubrication System The oil is then drawn into the pump suction. The pump increases the pressure of the oil and discharges it to the oil cooler. From the cooler outlet the oil flows, via fine filters, to the: ▪ Main bearings, ▪ Big-end bearing and Small-end bearing, ▪ Crosshead and Stuffing box (in case of large capacity compressors). SPMM.S1.0223.06 Compressors Version: 0.1 27 ADNOC Classification: Internal 1.2.1.4. COOLING IN RECIPROCATING COMPRESSORS Small capacity reciprocating compressors are typically air-cooled using a fan, which is an integral part of the belt drive flywheel. Cooling air blows across finned surfaces on the outside of the compressor cylinders. The fins increase the amount of radiating surface that is exposed to air, and which carries away much of the heat generated by compression. Air-cooled compressor requires adequate ventilation to perform reliably. Figure (1.33) Air Cooled Compressor Larger industrial reciprocating air compressors are water-cooled with a built-in cooling water jackets commonly around the cylinders, in the cylinder heads and stuffing box. Water-cooled compressors require an adequate pressure of quality water. Water-cooled units are more energy efficient. Figure (1.34) Water Cooled Compressor SPMM.S1.0223.06 Compressors Version: 0.1 28 ADNOC Classification: Internal 1.2.1.5. CAPACITY CONTROL Compressors requires regulate to their capacity against a given discharge pressure. There are two main reasons why compressor capacity control is used in reciprocating compressors: ▪ The most prevalent reason is to adjust the suction flow to match the process demand. ▪ The second reason is to save energy. The famous methods of capacity control use in reciprocating compressors are: ▪ Start-Stop ▪ Suction Line Throttling ▪ By-Pass Or Blow-Off Control ▪ Clearance Pocket Control ▪ Suction Valve Unloading START-STOP The compressor either delivers full output when running or nothing when stationary. This simple control is frequently used for plants requiring a low capacity and, in that case, it is usually automatic. Since the demand will seldom have only the extreme values of "full load" or "no load" a buffer tank (capacity) is installed between compressor and equipment, in which the pressure is allowed to fluctuate between certain limits. A pressure switch is provided to switch the compressor "on" when the pressure drops to the low limit and to switch it "off" again when the pressure reaches the high limit. Examples for this type of control are found on starting air compressors of small, compressed air plants etc. SUCTION LINE THROTTLING Suction line throttling is partially closing or pinching a valve in the compressor suction line. Throttling reduces volumetric efficiency and so acts to reduce the compressor capacity. This does however, not automatically mean that power requirement also goes down. SPMM.S1.0223.06 Compressors Version: 0.1 29 ADNOC Classification: Internal Figure (1.35) Capacity Control Using Suction Line Throttling BY-PASS OR BLOW-OFF CONTROL Bypass control as the name implies, this control method uses an external bypass around the compressor to recycle gas from the compressor discharge to the inlet, or to the atmosphere in the case of an air compressor. The take-off point for the bypass must be downstream of a heat exchanger so that cooled gas will be spilled back to the suction. If there is no exchanger in the discharge, the bypass must branch into the suction line upstream of an exchanger. Figure (1.36) Capacity Control Using Bypass Control CLEARANCE POCKET CONTROL Clearance pockets are used to add or remove internal volume within a compressor cylinder, by opening and closing the valve that separates the cylinder from the additional volume in the clearance pocket. SPMM.S1.0223.06 Compressors Version: 0.1 30 ADNOC Classification: Internal The effect of the clearance pocket is to decrease compressor capacity and power requirements. When the clearance volume of a compressor is excessive, no gas at all flows into the compressor. This condition, called shutoff. Figure (1.37) Capacity Control Using Clearance Pocket SUCTION VALVE UNLOADING Unloaders are control elements designed to hold suction valves open when they are activated, so that no gas can be trapped or compressed inside the cylinder during the compression cycle. Therefore, any compressor cylinders with activated unloaders will not be able to contribute any flow to the compressor’s total flow. Finger-Type Suction Valve Unloader Plug-Type Suction Valve Unloader Figure (1.38) Capacity Control Using Suction Valve Unloader SPMM.S1.0223.06 Compressors Version: 0.1 31 ADNOC Classification: Internal In the normal compression cycle, both the suction and the discharge valve are closed when the compression stroke begins. However, when a suction valve disc is held open during the compression stroke, gas will flow through the open valve back into the suction gas jacket. The valve may be held open manually (with a hand wheel) or pneumatically. The more unloaders that are activated the lower the total flow will be. Unloaders may be operated independently or in groups to produce the desired number of compressors “load steps.” Reciprocating compressors are often equipped with valve unloaders and clearance pockets as a means of controlling compressor throughput. If these flow control components malfunction, compressor flow may decrease dramatically or even drop to zero. Generally, as flow is decreased with the use of unloaders and/or clearance pockets, the required horsepower decreases. Conversely, as flow is increased with the use of unloaders and/or clearance pockets, the required horsepower increases. Figure (1.39) Double-Acting, Single-Stage, Horizontal Reciprocating Compressor with Plug-Type Unloader SPMM.S1.0223.06 Compressors Version: 0.1 32 ADNOC Classification: Internal 1.2.2. MAIN COMPONENTS AND PRINCIPLES OF CONSTRUCTION OF ROTARY COMPRESSOR Rotary compressors have a variety of uses in the oil and gas industry. They are often called blowers because they are used for moving large volumes of air through low compression ratio, thus a blower is a low ratio compressor. In rotary compressors, the displacement of the fluid is produced by the rotation of one or more elements within a stationary housing. Rotary compressors generally have no suction or discharge valves and use suction and discharge ports that are alternately exposed and covered by the rotating elements or sliding elements. Rotary compressors generally have smooth, pulse-free air output, in a compact size, with high output volume over a long life, and does not exhibit the shaking forces (no vibration). Each type of rotary compressor has different rotor design, size and operating range due to its unique structure. The most common types of rotary compressor found in the oil and gas industry are the: 1) Lobed Compressor (Blower) 2) Sliding Vane Compressor 3) Screw Compressor Rotary compressors are normally driven by electric motors or internal combustion engines, either through V-belts or by direct connection. 1.2.2.1. LOBED COMPRESSORS (BLOWER) Principle of operation of lobed blower Main Parts of Lobed Blower Figure (1.40) lobed Compressor (Blower) SPMM.S1.0223.06 Compressors Version: 0.1 33 ADNOC Classification: Internal Rotary twin-lobe compressors (blowers) consist of two rotors rotate in opposite directions inside elliptical casing houses and protects the internal parts. Each rotor has two or more lobes. The lobes are the rounded ends of the rotor. As the rotors rotate, they create a negative pressure at the intake, which draws air into the housing. As they revolve, the rotors carry the air along between the lobes and housing toward the discharge port. As the lobes mesh, the air is squeezed out of the discharge port. As the gas is displaced into the discharge port, the pressure of the gas increases. In a lobed blower there is a small clearance space between the lobes and the casing. The timing gears prevent the lobes from contacting. The rotors require no lubrication because they do not touch each other. In addition, the air temperature does not increase much, and the unit therefore requires little or no cooling. Because of the clearance space, some of the gas always leaks backwards. For this reason, they cannot be used to develop high discharge pressures. 1.2.2.2. SLIDING VANE COMPRESSOR A sliding vane compressor is a positive displacement machine rotary type, having a cylindrical slotted rotor with metallic sliding vanes inside an eccentric (off center) casing (housing). Figure (1.41) Sliding Vane Compressor SPMM.S1.0223.06 Compressors Version: 0.1 34 ADNOC Classification: Internal In the sliding vane compressor, the vanes slide in and out of the rotor under the action of centrifugal force produced by the rotation of rotor. In some design of this compressors, there are springs in the rotor slot help hold the vanes against the casing wall thus ensuring a gas tight seal against wall of casing. In this compressor, the air is picked-up at the inlet and trapped in the pockets between each pair of sliding vanes. Because the rotor is mounted off-center, the size of the pockets gets smaller as they get nearer to the discharge port. This action forces the air into a smaller volume. Displacing the air into a smaller volume increases its pressure. Sliding vane compressors require “flooded lubrication” because of the high potential for vane to housing contact, usually through a force-feed lubricators driven from the compressor shaft. 1.2.2.3. SCREW COMPRESSOR Rotary Screw air compressors are also positive displacement type units. However, instead of a piston, the rotary screw compressor increases pressure through the action of two intermeshing rotors within twin-bore housing. A. Compressor inter-lobe spaces being filled. B. Beginning of compression. C. Full compression of trapped gas. D. Beginning of discharge of compressed gas. E. Compressed gas fully discharged from inter-lobe spaces. Figure (1.42) Operation Principle of Screw Compressor In this compressor, air is trapped between the rotors and housing. As it moves along the rotor, air volume is decreased and pressure is increased because the allowable space for the trapped air is progressively reduced. Screw compressors are available in two basic types: ▪ Oil- flooded (wet type) and ▪ Oil-free (dry type). SPMM.S1.0223.06 Compressors Version: 0.1 35 ADNOC Classification: Internal I. Oil- flooded screw compressors (Wet) The oil-flooded rotary screw compressors (wet type) are the most common rotary air compressor. It’s commonly available as a single stage helical or spiral. In oil- flooded rotary screw compressors (wet type) oil is injected into the screw unit when compression takes place, and later the oil is siphoned out by an oil separator. But still there is a miniscule amount of oil carryover, it's the oil that is passed through the machine along with the compressed air and is missed by the separator. The oil in the oil-flooded type compressor lubricates and seals the rotors and acts as a coolant to remove the heat of compression. Since the cooling takes place immediately within the compressor, the moving parts never experience extreme operating temperatures. Oil-Flooded Rotary Screw Compressor Oil System of Oil-Flooded Rotary Screw Compressor Figure (1.43) Oil-Flooded Rotary Screw Compressor The oil-flooded type does not require timing gears as the oil film prevents contact of the rotors, one screw is driven by the prime mover, and then meshes with another screw. But an air-oil separator is necessary to remove the oil suspended in the compressed air as it leaves the compressor. This type of compressors is cheaper than the oil-free type, produce less noise, and they are less complicated to maintain. II. Oil-free rotary screw compressors (Dry) The oil free rotary screw air compressors (dry type) utilize specially designed air ends to compress air, without oil, in the compression chamber. They are used in situations and specific industry applications where the oil carryover, however negligible is a problem. SPMM.S1.0223.06 Compressors Version: 0.1 36 ADNOC Classification: Internal Since oil is not used to seal the rotors where compression takes place, there is some air loss or leakage. There is no oil to cool this 'dry" type compressor, so water jackets and after-coolers are often used to reduce the temperature of the compressor and the discharge air. The 'dry" type screw compressor will also use conventional moisture separators to trap the resulting condensation. Figure (1.44) Oil-Free Rotary Screw Compressor Dry type compressors require the use of timing gears to maintain the proper clearance between the rotors to prevent wear. These compressors require lubrication only for the timing gears and bearings. The oil free rotary screw air compressors (dry type) are more specialized and come at a higher cost. They also typically produce more noise and are required high maintenance. CAPACITY CONTROL FOR ROTARY COMPRESSORS Capacity control for rotary compressors is accomplished by variable speed drive or variable displacement. A slide valve is positioned in the casing for the latter control technique. As the compressor capacity is reduced, the slide valve opens, directing a portion of the compressed air back to the suction. SPMM.S1.0223.06 Compressors Version: 0.1 37 ADNOC Classification: Internal 1.2.3. AIR COMPRESSOR ACCESSORIES In order to work efficiently, most air compressors are equipped with several accessories. The common accessories normally attached to the air compressor are: ▪ Intake Filter ▪ Dryer ▪ Intercooler ▪ Condensate Trap ▪ Aftercooler ▪ Receiver ▪ Moisture Separators ▪ Air Line Filter Figure (1.45) Air Compressor Accessories INTAKE FILTER The intake filter removes solid particles (dust, dirt, and other contaminants) from the air before it is entering the compressor. The filter prevents these abrasives from causing premature wear to the cylinders, pistons, and rings. INTERCOOLER The intercooler is a heat exchanger (air cooled or water cooled) that placed between the stages of the multi-stage compressor. E.g., in two stage compressors, the intercooler cools the compressed air coming from the first stage, before it enters the second stage. AFTERCOOLER The aftercooler is also a heat exchanger (air cooled or water cooled). As its name implies, aftercooler cool the compressed air as it discharges from the compressor and before it goes into the air receiver. ❖ Single-stage compressors can only have aftercoolers but not intercoolers. ❖ Multi-stage compressors have intercoolers as well as aftercoolers. SPMM.S1.0223.06 Compressors Version: 0.1 38 ADNOC Classification: Internal MOISTURE SEPARATORS As the compression leaves the air hot and wet, then the intercooler and aftercooler lower the temperature of the air, thus the air cools and condensing water. Moisture Separators are used to remove water and other liquids (oil) from the compressed air. Generally, single-stage compressors have one moisture separator. But multi-stage compressors have moisture separators after each stage. DRYER Since moisture separators are never 100% effective, additional dryers are sometimes installed when extremely dry air is required. Dryer helps to eliminate any remaining moisture in the compressed air by using either a refrigerated condenser or a desiccant. Refrigerated condensers cool the air to condense water vapor into a liquid that is then drained from the system. Desiccants are powders or gels that remove water by absorbing it. CONDENSATE TRAP Condensate Trap collects and discharges liquid that condenses out of the air stream. Integral part of after coolers, dryers and separators RECEIVER Receiver stores a large reserve of compressed air to maintain a smooth flow to the plant. They typically have drain plugs to remove additional moisture that settles in the tank as the air cools and water vapor condenses. AIR LINE FILTER Air line Filter removes solids and liquids from the compressed air stream. Filters can be placed throughout the system. COMPRESSOR DRIVERS Compressor drivers include electric motors, steam turbines, or internal combustion engines. Drivers may be direct connected, connected through reduction gears, or belt connected. SPMM.S1.0223.06 Compressors Version: 0.1 39 ADNOC Classification: Internal 1.3 NORMAL OPERATING PARAMETERS & TOLERANCES FOR AIR COMPRESSORS Normal operating parameters and tolerances for air compressors are normally provided in the compressor manufacturers’ technical specifications/manuals. The compressor operating parameters could come in metric or imperial units, which include: ▪ Inlet Capacity (m3/h or CFM) (CFM = Cubic Foot per Minute) ▪ Maximum Discharge pressure (bar or PSI) ▪ Efficiency (%) ▪ Operating Speed (rpm) ▪ Maximum Power (MW or HP) The tables in the next pages show summary of typical operating parameters for all type of compressors. Pressure is the main parameter of compressed air which is usually expressed in the unit’s 5 5 2 psi or bar (psi = pounds/sq-inch); 1 bar = 10 Pa = 10 N/m = 14.504 psi). ▪ Low (0 to 150 psi) ▪ Medium (151 to 1000 psi) ▪ High (over 1000 psi) Compression ratio is the ratio between the compressor discharge pressure and the compressor suction pressure. If the discharge pressure is 20 psig and the suction pressure is 5 psig, then the compression ratio is 4:1. That is, 20 divided by 5. Compressor capacity is the volume of gas passing through the machine in a given period of time. TOLERANCES Tolerances of this operating parameters are normally provided as percentage (± %) in the compressor manufacturers’ technical specifications/manuals. If these tolerances are exceeded for long period of time, the recommended operating parameters from the manufacturer will be affected and the compressor’s parts will be negatively impacted. SPMM.S1.0223.06 Compressors Version: 0.1 40 ADNOC Classification: Internal Table (1.1) Summary of Typical Operating Parameters for of Compressors (Metric) SPMM.S1.0223.06 Compressors Version: 0.1 41 ADNOC Classification: Internal Table (1.2) Summary of Typical Operating Parameters for of Compressors (Imperial Units) SPMM.S1.0223.06 Compressors Version: 0.1 42 ADNOC Classification: Internal 1.4 MAIN DIFFERENCES BETWEEN RECIPROCATING AIR COMPRESSORS AND ROTARY AIR COMPRESSORS Comparison between Reciprocating and Rotary air compressors can be done in aspects like pressure ratio, handled volume, speed of compressor, vibrational problem, size, air supply, purity of compressed air, compression efficiency, maintenance, mechanical efficiency, lubrication, initial cost, flexibility and suitability. No. Aspect Reciprocating Compressors Rotary Compressors Discharge Pressure of air is high. Discharge pressure of air is low. 1 Pressure Ratio The pressure ratio per stage will be in the order of 4 to 7. The pressure ratio per stage will be in the order of 3 to 5. Large measure of air handled can be handled and it is 2 Handled Volume Quantity of air handled is low and is limited to 50 m3/s. about 500 m3/s. 3 Speed of Compressor Low speed. High. Due to reciprocating section, greater vibrational problem, Rotary parts of machine, thus it has less vibrational 4 Vibrational Problem the parts of machine are poorly balanced. problems. The machine parts are fairly balanced. 5 Size of compressor Size of Compressor is bulky for given discharge volume. Compressor size is small for given discharge volume. 6 Air supply Air supply is intermittent. Air supply is steady and continuous. Air delivered from the compressor is dirty, since it comes in Air delivered from the compressor is clean and free from 7 Purity of compressed air contact with lubricating oil and cylinder surface. dirt. 8 Compressed efficiency Higher with pressure ratio more than 2. Higher with compression ratio less than 2. 9 Maintenance Higher due to reciprocating parts. Lower due to less sliding parts. 10 Mechanical Efficiency Lower due to several sliding parts. Higher due to less sliding parts. SPMM.S1.0223.06 Compressors Version: 0.1 43 ADNOC Classification: Internal No. Aspect Reciprocating Compressors Rotary Compressors 11 Lubrication Complicated lubrication system. Simple lubrication system. 12 Initial cost Higher. Lower. 13 Flexibility Greater flexibility in capacity and pressure range. No flexibility in capacity and pressure range. For medium and high-pressure ratio. For low and medium pressures. 14 Suitability For low and medium gas volume. For large volumes. Example for the 15 Compressor Table (1.3) Summary of the Main Differences between Reciprocating Air Compressors & Rotary Air Compressors SPMM.S1.0223.06 Compressors Version: 0.1 44 ADNOC Classification: Internal 1.5 DIFFERENT SEAL TYPES FOR WET SEAL OIL SYSTEMS & DRY GAS SEALS Seals are devices that used between moving and stationary parts to separate, and minimize leakage between, areas of unequal pressures. Compressor seals restrict or prevent process gas leaks to the atmosphere or seal fluid leaks into the process stream over a specified operating range, including start-up and shut-down conditions. Depending on the application, the seals may be of a dry or liquid lubricated type. Seals type also depends on whether the shaft is rotating or a reciprocating (piston rod). Seals may require a buffer gas, seal oil, or both to enhance the sealing function. If gas handled by a compressor causes contamination, chemical reaction or any other deterioration of oil, sealing systems should completely isolate gas from lubrication. 1.5.1. SEAL FOR RECIPROCATING COMPRESSORS As discussed before, packing rings are used in reciprocating compressors to control gas leakage from the cylinders. The packing gland contains a series of segmented packing rings around the piston rod. When the compressor is handling toxic or flammable gas; a purge gas, such as nitrogen, may be used to provide a positive seal from the atmosphere and improve the venting of the process gas from the sealing area. The leakage is typically vented to a low-pressure vent system or to a low-pressure flare header. Care should be exercised to ensure that the packing gland pressure is compatible with the flare header pressure. 1.5.2. SEAL FOR ROTARY COMPRESSORS The rotor shafts of rotary compressors are usually provided with labyrinth seals, or mechanical seals, or dry gas seal. As discussed before, rotary compressors are available in both oil injected and oil free types. Oil injected rotary compressors (sliding vane compressors and wet type screw compressors) the oil seals the internal clearances and seals are provided at the drive shaft to prevent process gas leaks to the atmosphere. Oil free rotary compressors especially the dry type of screw compressors, seals are provided to prevent process gas leaks to the atmosphere and to seal lubrication oil from leaks into the gas side. SPMM.S1.0223.06 Compressors Version: 0.1 45 ADNOC Classification: Internal 1) LABYRINTH SEALS The labyrinth seal is a special type of seal, used in screw compressors and turbomachinery for sealing purpose. Labyrinth seal is a non-contacting type seal that uses a tortuous path to minimize the gas leakage. They are usually made of a soft material such as bronze, babbitt, or aluminum. A series of grooves are machined to sharp edges that maintain a close clearance between the mating parts. Labyrinth seals should be used where high leakage rate can be managed or tolerated. Labyrinth seals have no pressure or speed limits and may incorporate buffer gas usually inert gas to further ensure separation of the process from the sealing medium. Labyrinth Seals Buffer Gas Supply Labyrinth Seals without Buffer Gas Supply Figure (1.46) Labyrinth Seals 2) MECHANICAL SEALS Mechanical seals also called contact seals, consist of machined rotating and stationary surfaces. The surfaces are in direct contact with each other to prevent any leakage. They are mainly used for low pressure gas that is not corrosive. A common type of mechanical seal has a rotating contact ring, a full floating wear ring, a stationary ring, and a spring loading device. A small amount of lubricating oil is used to remove any friction SPMM.S1.0223.06 Compressors Version: 0.1 46 ADNOC Classification: Internal Mechanical Seals Operation Principle Oil-Injected Screw Compressor With Mechanical Seal Figure (1.47) Mechanical Seals 3) DRY GAS SEALS Oil-free compressors are most often used in process gas applications. Hazardous, poisonous or simply dangerous gases are usually being compressed and conveyed mainly by Oil-free screw compressors. It is critical therefore, that such conveying media be sealed against leaks to the atmosphere or, in the case of gases incompatible with lubrication oils, against leaks into the compressor's lubrication system. Dry gas sealing systems are often applied for such tasks. SPMM.S1.0223.06 Compressors Version: 0.1 47 ADNOC Classification: Internal Figure (1.48) Typical layout of Screw Compressor with Dry Gas Seal Dry gas seals are mechanical face seals. They consist of a stationary (primary) ring and a mating, rotating ring. During operation, grooves in the mating ring generate fluid- induced dynamic forces, causing the primary ring to separate from the mating ring, thus creating a gap between them. A typical value of the running gap between the primary and mating rings is 3 to 4 microns. A sealing gas in injected into the seal, providing the seal between the atmosphere (or the oil system of the compressor) and the compressor's conveying chamber. Typically, a labyrinth seal separates the gas seal from the process gas, while a barrier seal, also a labyrinth seal, separates the gas seal from the compressor's bearings and their oil lubrication system. Barrier seals are buffered with gas - typically nitrogen, at a fixed pressure, and vented to the same vent as the seal gas exiting the dry gas seals. Dry Gas Seal Operation Principle Oil-Free Screw Compressor with Dry Gas Seal Figure (1.49) Dry Gas Seal SPMM.S1.0223.06 Compressors Version: 0.1 48 ADNOC Classification: Internal 2. ROUTINE MAINTENANCE TECHNIQUES FOR AIR COMPRESSORS 2.1 TYPICAL ELECTRICAL & MECHANICAL FAULTS FOR AIR COMPRESSORS The typical electrical and mechanical faults for air compressors are general guide in nature. Depending upon the compressor type, its operating conditions or its application, some of these symptoms and their possible causes may not apply. It is therefore essential that maintenance personnel be completely familiar with their machine, its processes and operating conditions. Fault Possible Cause(s) Failure to deliver Excessive clearance between vanes, lobes or screws (rotary compressors). output Worn or broken valves and/or defective unloader(s) (reciprocating compressors). Insufficient output Restricted or dirty inlet filter. or low pressure Excessive leakage (air system). Inadequate speed. Worn or damaged piston rings (vanes, lobes or screws on rotary systems). System demand exceeds capacity. Worn valves or defective unloader(s). Compressor Carbon deposits on discharge valves. overheats Excessive discharge pressure. Worn or broken valves. Excessive speed. Inadequate cooling. Dirty cylinder water jackets. Inadequate cylinder lubrication. Defective unloader(s). Compressor Piping improperly supported causing resonance. vibrates Misalignment at coupling. Loose flywheel or pulleys (where used). Defective unloader(s). Unbalanced motor or defective motor bearings. Inadequate cylinder lubrication. Loose base plate mounting bolts or soft foot. Incorrect speed. Damaged foundation or grouting. Excessive discharge pressure. Worn or damaged rotating components (rotary compressors). Excessive receiver Defective unloader(s). pressure Excessive discharge pressure. High oil Oil level too high. consumption Faulty gas/oil separator (rotary compressors). Scavenger tubes plugged. Oil leaks at gaskets, seals or fittings. Excessive oil pumping (reciprocating compressors). SPMM.S1.0223.06 Compressors Version: 0.1 49 ADNOC Classification: Internal Fault Possible Cause(s) Excessive Worn or broken valves, second stage. intercooler Defective unloader, second stage. pressure Low intercooler Worn or broken valves, first stage. pressure Defective unloader, first stage. Dirty or restricted inlet filter or suction line. Worn piston rings on low pressure (first stage) piston. Worn rotating components (rotary compressors). Compressor Inadequate lubrication. knocks Insufficient head clearance. Excessive crosshead clearance. Loose piston rod(s). Excessive bearing clearance. Loose or damaged piston(s) (reciprocating compressors). Loose flywheel or drive pulley (where used). Misalignment at coupling. Damaged foundation or grouting. Loose motor rotor or shaft. High discharge Carbon deposits on discharge valves. temperature Worn or broken valves. Defective unloader(s). Excessive discharge pressure. Inadequate cooling. Dirty water jackets (or plugged or dirty fins on air-cooled compressors). Dirty or plugged intercooler. Abnormal (high) intercooler pressure. Inadequate cylinder lubrication. Cooling water Low level of coolant. discharge Dirty water jackets. temperature Worn or broken valves. Too high Defective unloader(s). Excessive discharge pressure. Dirty or corroded intercooler. Abnormal intercooler pressure. Valves overheat Excessive discharge pressure. Long unloaded cycles (inlet valves). Damaged or carbonized valves. Defective unloader(s). High levels of Excessive discharge pressure. condensate Excessive discharge temperature. Inoperative intercooler. Plugged or inoperative heat exchanger or water separator. Compressor seals Excessive operating temperatures. fail prematurely Lubricant incompatible with seal materials. Misalignment at coupling. Excessive crank case pressure. Seal material incompatible with the gas being processed. SPMM.S1.0223.06 Compressors Version: 0.1 50 ADNOC Classification: Internal Fault Possible Cause(s) Drive motor Inadequately sized motor. overheats Excessive discharge pressure. Worn or broken valves. Abnormal intercooler pressure. Inadequate lubrication (compressor running gear or motor bearings). Misalignment at coupling. Excessive belt tension (where used). Low voltage. Premature oil Excessive lubricant operating temperature. thickening or Compressor operating temperature too high. discoloration Inadequate lubricant type (wrong oil for the application). Worn or faulty piston rings. Excessive discharge temperature. Lubricant oxidation. Table (2.1) Typical Electrical and Mechanical Faults for Air Compressors 2.2 COMMON SIGNS OF DAMAGE, WEAR & CORROSION FOR AIR COMPRESSORS Air compressors are an integral part of many industries. When air compressor stops working as efficiently as it should or stops working altogether, the problems can cause delays, necessitate expensive services, or even put the employees in danger. One of the best ways to prevent serious air compressor issues is to handle repairs as soon as they are needed. Here are some warning signs that indicate that your air compressor needs to be inspected and may need to be repaired. COMPRESSOR LEAKAGE Any leakage from air compressor is a red flag. Excessive pressure, temperature or corrosion can loosen the seals and joints, letting fluid escape. Fixing a leaking air compressor may be as simple as tightening the fasteners around the joint. In other cases, the mechanical seal or gasket may need replacing. UNUSUAL NOISES AND/OR VIBRATION Industrial air compressors are loud, but any compressor unit should only make one type of noise that continues at a consistent volume. If the air compressor suddenly becomes louder, there may be an issue with the compressor or motor. If the sound of the compressor changes to include rattling, humming, or screeching, compressor may have a loose, broken or a foreign component that needs to be replaced. SPMM.S1.0223.06 Compressors Version: 0.1 51 ADNOC Classification: Internal FREQUENT THERMAL OVERLOAD (OVERHEATING) If a compressor shuts down on thermal overload check for proper ventilation around the compressor. Clean any coolers. Reset the thermal overload. If this step does not eliminate the problem, further inspection on the compressor must be carried on. Additionally, if the compressor overheats often, it may need to be serviced. LOW FLOW A healthy air compressor performs at about the same level every time it’s used. Any change in performance could indicate a system problem. Check to see if there is an excessive air leak in the system. Has additional equipment or demand been added? If nothing in the system has changed then the compressor may have internal problems such as worn piston rings or valves or faulty system. LOW AIR PRESSURE Low air pressure is one of the most common issues with faulty compressors. This decrease in pressure can make the compressor unit impossible to use. In many cases, low air pressure is related to faulty controls. However, inadequate air pressure can also result from internal compressor wear or something as simple as slipped belts. NO AIR PRESSURE If the compressor has no air pressure at all, the compressor most likely has a control problem. Check the controls for proper settings. If the problem persists, further inspection must be carried out on the compressor and controls. OILY AIR DISCHARGE As most air compressor needs oil lubricant to run correctly. Depending on the type of compressor some oil will carry over to the discharge. However, if the oil carries over has increased the air compressor may have internal or control issues. SPMM.S1.0223.06 Compressors Version: 0.1 52 ADNOC Classification: Internal 2.3 TYPICAL PLANNED & PREVENTATIVE MAINTENANCE FOR AIR COMPRESSORS Maintenance is essential to provide for the company and the work force both safe and dependable plant and equipment. The diagram below illustrates the various types of maintenance. Preventive maintenance (PM): is the maintenance performed according to a fixed schedule based on elapsed time or meter readings, involving the routine repair and replacement of machine parts and components. The intent of PM is to “prevent” maintenance problems or failures before they take place by following routine and comprehensive maintenance procedures. Maintenance schedule: is a comprehensive list of items and the maintenance required, including the intervals at which maintenance should be performed. Scheduled maintenance includes operations such as: 1. Cleaning 6. Reconditioning/Overhaul 2. Lubrication 7. Replacement of Life Components 3. Replenishing 4. Adjustment 5. Testing and Inspection SPMM.S1.0223.06 Compressors Version: 0.1 53 ADNOC Classification: Internal The organization and administration of resources required to undertake any maintenance programs include: a. Tools, test equipment, workshop facilities and equipment. b. Spare parts, stock materials and consumables. c. Personnel, both internal and external. d. Reference data and documentation. e. The work plans. f. Reporting procedures. Normally the manufacturer’s operation and maintenance manual give details of all maintenance schedules and will indicate the required specific checks and the intervals to assure the maximum performance and service life of the air compressor. The following is a typical planned and preventative maintenance for air compressors. Recommended Interval Turnaround Overhaul/ Biannual Monthly Equipment Maintenance Task 5 Years Weekly Annual General 1. Foundation Examine concrete for cracks and spalling. √ 2. Frame Examine metal for corrosion and cracks. √ Clean and paint as required. 3. Compressor Check V-belts for slippage, chains for looseness, and √ Drive shaft couplings for excessive runout or vibration. Dress or tighten V-belts as required. Tighten coupling bolts and lubricate coupling as required. Check V-belts for signs of wear or aging and replace √ as needed. Check shaft runout of direct coupled machines with dial indicator and check shaft alignment if runout is excessive. 4. Cooling Check flow of water or coolant through compressor √ System and after-cooler. Check for accumulation of dirt and lint on cooling fins of air-cooled compressors and radiators or water- cooled compressors. Check for corrosion and scale buildup and clean or √ flush as required. Thoroughly clean cooling fins of air-cooled compressors and radiators of water-cooled compressors. 5. Air Intake Check condition of filter and intake for obstructions. √ √ and Filter Replace filter as required. 6. Piping and Check piping for corrosion. √ Valves Clean and repaint or replace piping as required. Repack and reseat valves as required. SPMM.S1.0223.06 Compressors Version: 0.1 54 ADNOC Classification: Internal Recommended Interval Turnaround Overhaul/ Equipment Maintenance Task Biannual Monthly 5 Years Weekly Annual 7. After- Check for leaks and for adequate water flow. √ coolers Disassemble and check for internal corrosion and scale buildup. Clean as required. 8. Separators Check for leaks. √ Disassemble and check for corrosion and scale buildup. Clean as required. 9. Traps Operate manual drains. √ Check automatic traps for leaks and proper operation. √ Clean strainer and check for corrosion or scale buildup 10. Dryers Replace dryer elements as required on deliquescent √ dryers. Check operation of refrigerated and desiccant types. 11. Pressure Check operation and verify that regulating valves are √ Regulating providing correct pressure downstream from valve. Valves 12. Pressure Verify operation and setting. Check for signs of √ Relief Valves leaking, rust or corrosion, deposits, or mineral buildup. Perform operational test of relief valve either in service √ or remove and perform test on test stand. 13. Receiver On air receiver tanks, open the receiver drain valve √ Tanks and blow down until water is removed from tank. Check for leaks on all pressure vessels. Make thorough inspection of exterior of the tank, √ paying close attention to joints, seams, and fittings. All receiver tanks are to be inspected in accordance √ pressure vessel Standards. 14. Gauges Check operation of gauge. √ Look for loose or stuck pointer. If there is any doubt about the accuracy of gauge, remove and check calibration or replace with new gauge. Remove gauge and calibrate. √ Make any necessary repairs or replace with new gauge if gauge is not repairable. 15. Pressure & See that pressure switches cut in and out at proper √ Temperature pressures. Check setting of temperature switches. Switches Check switch calibration and set points. √ 16. Unloader Check that compressor is not being loaded until √ operating speed is reached in starting and that it unloads at the proper pressure. Inspect valves and air lines for leaks and valves for √ proper seating. Lap valves if required. Examine solenoid for deteriorated insulation or loose connections. SPMM.S1.0223.06 Compressors Version: 0.1 55 ADNOC Classification: Internal Recommended Interval Equipment Maintenance Task Turnaround Overhaul/ Biannual Monthly 5 Years Weekly Annual 17. Bearings Check antifriction bearing for excessive vibration or √ noise and schedule replacement as required. Check for adequate lubrication. Disassemble compressor and inspect condition of all √ bushings and babbitt-lined bearings. Repair or replace as required. Reciprocating Compressors 18. Lubrication Check that oil or grease cups are full and that crank √ case oil is at proper level. Replace or add the correct lubricant to bring to proper levels in crankcase or oil reservoir. Check oil feed rate to cylinder. Check forced oil systems for proper operation. Note any leaks and repair if excessive. Clean oil or grease cups and piping. Check condition √ of lubricant and change if required. 19. Packing Check for excessive leakage and for scoring on piston √ Gland rod. Adjust packing as necessary. Replace packing as necessary. √ 20. Crosshead If visible, check fit and lubrication. √ Check bearing shoes for scoring and wear and fit to √ crosshead. Shim shoes, if necessary, to obtain proper fit. Check pin and bushing for wear and replace or refit as required. 21. Cylinder Check cylinder walls for wear and scoring. √ Measure inside diameters at top, bottom, and middle in two directions, 90 degrees apart. If cylinder is out-of- round or oversized, re-bore cylinder. 22. Piston Check piston for wear. √ Check clearance with micrometer. Examine rings for tightness and fit. Replace if necessary. Check piston rod for trueness and scoring or wear. Renew or replace as required. 23. Connecting Check for distortion or bending. √ Rod Check bearing bolts and nuts for damage and replace as required. 24. Intake and Inspect valves and seats for scoring and proper √ Discharge seating. Valves Not Clean any deposits off of seats and valve plates, being very careful not to scratch the surfaces. Lap valve seats if there are any imperfections. Note: Deposits on the valves indicate a dirty intake, the wrong type or excessive oil, or a leaking valve or valve gasket. SPMM.S1.0223.06 Compressors Version: 0.1 56 ADNOC Classification: Internal Recommended Interval Turnaround Overhaul/ Equipment Maintenance Task Biannual Monthly 5 Years Weekly Annual Rotary Screw Compressors 25. Air End Check condition of rotors and bearings. Replace if worn or if compressor efficiency has √

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