Marine Boiler Water Management. PDF

Chapter 1 Marine Boiler Water Management 010 1 Marine Boiler Water Management Importance of marine boiler water quality management Treatment of water used for marine boiler plants is conducted for the following purposes: (1) Scale prevention (2) Corrosion prevention (3) Carry-over prevention...

Chapter 1 Marine Boiler Water Management 010 1 Marine Boiler Water Management Importance of marine boiler water quality management Treatment of water used for marine boiler plants is conducted for the following purposes: (1) Scale prevention (2) Corrosion prevention (3) Carry-over prevention Management of boiler plant water quality is an important duty for operators of marine boilers. As part of their normal duties, operators must: carefully analyze feed water/condensate and boiler water; determine a course of action based on the results of this analysis; and then take the steps dictated by the course of action. When analysis results dif fer from predicted values – even if the results fall within acceptable limits – the cause of the discrepancy must be investigated. To ensure that their vessel is always supplied with water that meets operational requirements, the marine boiler operator responsible for water quality must demonstrate comprehensive knowledge of the principles of boiler plant water quality. FO SETT TK 46°C 136°C 61°C METAL METAL 91°C 53°C 70°C 212°C 58°C 109°C FROM FOTANKS BURNG PUMP 2.184MPa NO1 SH STM 0.507MPa 75°C HEADER 0.947MPa (S) 44°C NO2 SH STM 2.089MPa 422°C ASSIST STM 0.165MPa 38°C (P) S W TEMP 25°C E /R TEMP 45°C DSH STM 2.037MPa 51°C AIR FWC 184kPA NO.2 BLR 2 0.568MPa AIR -12kPA FEED WTR 3.021MPa 179°C NO.1 BLR FO CONSUMPTION ASSIST STM 0.002MPa HEADER 0.058MPa 1 STM FO HTR 3.672MPa 108°C 1094L/4HR Fig.1 2 Marine boiler overview 2-1 Marine boiler types Ships use the following types of steam generators and each has a specific purpose: 1) Auxiliary boilers (1MPaG class or less) Auxiliary boilers for common diesel ships produce 0.7MPaG-class saturated steam that is used to operate auxiliary machinery and equipment; to heat fuel oil, lubricating oil and fresh water; and for air-conditioning equipment, galley and miscellaneous purposes. ① Vertical Cylindrical Smoke Tube Boiler • Standard design pressure: 0.8MPaG • Furnace: Full water-cooled type (~ 7,000 kg/h) • Evaporation: 600 ~ 1,500 kg/h • Heating surface: Smoke tube BURNING GAS OUTLET STEAM SPACE N. W. L. INSULATION SMOKE TUBE MANHOKE BRTNER FURNACE Fig.2 011 Marine Boiler Water Management Water management criteria vary according to boiler working pressure. Marine boilers are broadly classified into three groups based on working pressure: main boilers for steam turbine ships (for LNG tankers); auxiliary boilers for diesel ships (for very large crude oil carriers – VLCCs); and auxiliary boilers for general diesel ships. The recent trend toward increasingly more sophisticated and complex marine boilers has highlighted the importance of boiler water quality management. To prevent accidents resulting from boiler plant water, you must understand the importance of water treatment – because doing so will allow you to ensure that feed water, condensate and boiler water all meet the requisite quality standards. You must also be able to acquire the practical knowledge and ability required to manage and maintain water quality. Please note that the main boiler feed water/condensate for turbine ships is used in a closed system. As such, integrated management and control of water quality is imperative if turbine plant accidents are to be prevented. Chapter Marine Boiler Water Management 012 1 ② Vertical Cylindrical Smoke Tube Composite Boiler • Standard design pressure: 0.8MPaG • Furnace: Full water-cooled type • Evaporation – Oil firing side: 300 ~ 3,000 kg/h – Exhaust gas side: 300 ~ 3,000 kg/h • Heating surface: Smoke tube (For both the oil firing and exhaust gas sides) M/E EXH. GAS OUTLET BURNING GAS OUTLET CLEANING HOLE STEAM SPACE N. W. L. SMOKE TUBE SMOLE TUBE MANHOKE INSULATION BURNER FURNACE CLEANING HOLE M/E EXH. GAS INTLET Fig.3 ③ Vertical Cylindrical Water Tube Composite Boiler • Standard design pressure: 0.8MPaG • Furnace: Large combustion chamber with base of refractory material at its bottom • Evaporation – Oil firing side: 1,200 ~ 1,500 kg/h – Exhaust gas side: 950 ~ 1,500 kg/h OE VC 2 .a i STEAM SPACE INSULATION M/E EXH, GAS OUTLET MANHOLE WATER TUBE M/E EXH, GAS INLET N. W. L. SMOKE BOX SMOKE BOX CLEANING HOLE CLEANING HOLE MANHOLE BURNING GAS OUTLET SMOKE BOX CLEANING DOOR WATER TUBE DOWNCOMER TUBE FURNACE BURNER Fig.4 OEV.ai Marine Boiler Water Management STEAM SPACE INSULATION BURNING GAS OUTLET MANHOKE N. W. L. CLEANING HOLE CLEANING DOOR SMOKE BOX WATER TUBE 013 DOWNCOMER TUBE MANHOLE FURNACE Fig.5 ④ Vertical Cylindrical Water Tube Boiler • Standard design pressure: 0.8MPaG • Waste oil incinerator: Optional • Furnace: Large combustion chamber with base of refractory material at its bottom • Evaporation: 1,000 ~ 1,800 kg/h 2) Auxiliary boilers (2MPaG class) Auxiliary boilers for diesel VLCCs (double-drum water tube boilers without superheaters) Double-drum water tube boilers produce steam in the 1.57 ~ 2.0MPaG pressure spectrum that is used to drive cargo oil pump turbines. This type of boiler has two or more different operating modes and adjustable pressure settings for use at sea and in port (for loading/unloading). Gas Outlet Steam Outlet F.O.Burner Steam Separator Wind Box Combustion Air Inlet Steam Drum Generating Tube Soot Blower Partition water wall Combustion Gas Flow Baffle Plate Screen Tube Front (Rear) Wall Tube Water Drum Fig.6 Fig.6 shows a Mitsubishi MAC-B auxiliary boiler. Its main specifications (MAC-B 80 Tanker Mode) are: • Steam pressure: 1.57MPa • Max. evaporation: 82,000 kg/h • Steam temperature: 203.4˚C (SAT) Marine Boiler Water Management BURNER Chapter 1 3) Main boilers (6MPaG class) Main boilers (6.0MPaG×525˚C, 6.2MPaG×515˚C, etc.) for steam turbine ships are mainly used on LNG carriers. Superheated steam tube Combustion Chamber Steam drum Furnace Marine Boiler Water Management 014 Downcomer Water drum Fig.7 Fig.7 shows the model of Kawasaki Heavy Industries’ marine boiler UMG 17/14. • Steam pressure: 41.5 kg/cm2 • Steam temperature: 454˚C • Max. evaporation: 17,000 kg/h Marine Boiler Water Management 4) Fin tube-type exhaust gas economizer The fin tube-type exhaust gas economizer is used to recover thermal energy from the exhaust gas of a large main diesel engine; and to generate saturated steam and superheated steam that it supplies to the turbo generator system. 015 • Exhaust gas boiler and exhaust gas economizer • Forced-circulation water tube type exhaust gas economizer A tube (bare or spiral) is located in the exhaust gas flue. When the main engine is being run, a boiler water circulation pump – found between the exhaust gas economizer and the auxiliary boiler – is used to recover heat and generate steam. Large systems, meanwhile, feature a low-pressure steam generator, a high-pressure steam generator and a superheater between the exhaust gas outlet and exhaust gas inlet. M/E EXH. GAS OUTLET S/G OUTLET HEADER MANHOKE S/G INLET HEADER S/H INLET HEADER INSPECTION HOLE S/H OUTLET HEADER INSULATION M/E EXH. GAS INLET Fig.8 Marine Boiler Water Management These are found in the exhaust gas flue, where they are used to recover residual heat from the exhaust gas of the main diesel engine. The exhaust gas economizer is connected to the auxiliary boiler and uses the latter’s drum to separate steam from water. Meanwhile, the exhaust gas boiler has its own drum for separating steam. Chapter 016 1 2-2 Marine boiler plants 2 - 2 -1 Auxiliary boilers (1MPaG class or below) Auxiliary boilers for common diesel ships (for 0.7MPaG saturated steam) Marine Boiler Water Management Steam & Feed Water Flow for Diesel Ship(1).ai 2013_01_26 1) Steam and feed water flow diagram • Steam & Feed Water Flow for Diesel Ship(1) 0.6MPaG Saturated Steam Accomodation F.O./L.O. Tank Heating Aux. Boiler (Composite) & E.G.E. F.O. Heaters F.O. Storage Tank Steam Trace Others Main Eng. Exh. Gas Sampling Overboard Aux. Condenser To Clean Drain Tank Chemical Injection Tank F Inspection Tank Cascade Tank To Bilge Tank P Boiler Feed Water Pump F.W. Pressure Tank F.W. Tank Fresh Water Generator Fig.9 The Fig. above shows the steam and feed water flow diagram for a composite boiler. Saturated steam generated by the auxiliary boiler (while in port and reheating while at sea) or by the exhaust gas economizer (exhaust gas from the main engine while at sea) is used as a heat source for fuel oil (FO) and lubricating oil (LO) tanks, for heating FO pipes and for galley use, and its drain returns to the cascade tank via the auxiliary condenser and the inspection tanak. You can confirm the presence/absence of oil content on the inspection tank surface. Drain accumulates in the cascade tank, and shortages, if any, are made up for with fresh (distilled) water from the fresh water pressure tank, which is conveyed to the auxiliary boiler by the feed water pump via a feed water control valve. Boiler compounds are injected either by a chemicals feeder prior to feed water pumping, or are injected directly into the cascade tank after being dissolved. Proper boiler water management includes sample testing, followed as necessary, by blowing off of boiler water and/or injecting of boiler compounds. Marine Boiler Water Management As shown in Fig.10 below, there is also a system for independently setting an auxiliary boiler and exhaust gas economizer. This system, used at sea, generates steam with the auxiliary boiler by means of a boiler water circulation pump that circulates boiler water between the boiler and economizer. 017 • Steam & Feed Water Flow for Diesel Ship (2) Drain Steam E.G.E Aux. Boiler Marine Boiler Water Management FO/LO Heating etc Drain Cooler Chemical F Inspection Tank Main Engine Exh. Gas Boiler Water Cir.Pump Overboard Cascade Tank Fead Water Pump Sampling F.W. Pressure Tank F.W. Tank F.W. Generator Fig.10 2) Boiler water quality management procedures and related equipment ① Injection of boiler compounds If deemed necessary following boiler water testing, dissolve boiler compounds and inject them into the cascade tank. ② Sampling Take a boiler water sample from the piping attached to the auxiliary boiler, and place it into the dedicated container. ③ Inspection tank In the drain (superheated steam, etc.) return line, an inspection tank has been placed on this side of the cascade tank; look into the tank to confirm the presence/absence of floating matter (oil, etc.). ④ Blow-off pipe Based on the results of the boiler water test, you can drain boiler water overboard to reduce enrichment or remove impurities. Chapter 1 2-2-2 Auxiliary boilers (2.0MPaG class) Auxiliary boilers for diesel VLCCs (double-drum water tube boilers without superheaters) (Used for driving cargo oil pump turbines; 1.57MPaG saturated steam) Marine Boiler Water Management 018 1) Steam and feed water flow diagram • Steam & Feed Water Flow Diagram for Diesel Ships (VLCCs) SLOP TANK C CARGO OIL STRIP PUMP D WORK SHOP AUX. BOILER AIR EJECTOR SC 1.57/0.92 TO SOOT BLOWER SAMPLE COOLER ATOMIZING STEAM PURGE STEAM TANK CLEAN PUMP TURBINE AIR EJECTOR COND. NO.1 CARGO OIL PUMP TURBINE B AUX. COND. 0.92/0.29 MPaG F.O./L.O. TANK HEATING COMPOUND TANK NO.3 CARGO OIL PUMP TURBINE ATMOS. COND. DISTILLED WATER TANK SUPER HEATER SC A EXHAUST GAS VACUUM PUMP CONDENSATE PUMP D EXHAUST GAS ECONOMIZER (E.G.E.) (EGE) 0.29 MPaG NO.2 CARGO OIL PUMP TURBINE P C OTHERS H.P.EVAPORATOR 0.92 MPaG F.O. HEATER F.O. SERV./SETT. TANK L.P.EVAPORATOR A SC ACCOMODATION STEAM SEPA. DRUM T/G F.W. B INSPECTION TANK P CASCADE TANK HYDRAZINE TANK & PUMP P T/G COND. TO E.G.E. CLEANING T/G CONDS.PUMP SC H.P. BOILER W. CIRC. PUMP P P L.P. BOILER W. CIRC. PUMP OVER BOARD P SC :SALINITY INDICATOR CELL EGE I ST STAGE FEED WATER HEATER :CONTROL VALVE AUX. FEED PUMP FRESH WATER GEN. F.W.TANK DRINKING WATER TANK 2ND STAGE FEED WATER HEATER P (Sterilizer) FEED PUMP Fig.11 Feed water is supplied to the cascade tank from the distilled water tank, where low-salt (10ppm or less) distilled water produced by the onboard distilling plant is stored. While at sea, this boiler is operated in exhaust gas economizer (EGE) mode. Saturated steam generated by the auxiliary boiler passes through the EGE superheater to become superheated steam, which is then supplied to the turbo generator (T/G). Pressure-reduced saturated steam, meanwhile, is used for heating the FO/LO and water. Exhaust gas from T/G is seawater-cooled into condensate in the vacuum T/G condenser and then pumped back into the cascade tank by the T/G condenser pump, returning via the feed water heater. Marine Boiler Water Management Steam used for heating is returned to the atmospheric condenser, seawater-cooled into drain and then returned to the cascade tank via the inspection tank. The auxiliary feed pump moves feed water from the cascade tank via the second stage feed heater and the feed water control valve to either the steam separator drum or the auxiliary boiler. Exhaust gas from the main diesel engine is used to heat the evaporators, producing lowpressure steam in the low-pressure steam separator drum and medium-pressure steam in the auxiliary boiler. This steam is then supplied where it is needed. When the vessel is in port undergoing cargo operations, the boiler is operated in tanker mode (pressure setting: 1.57MPaG) and saturated steam is used both to drive the cargo oil pump turbines to unload cargo (crude oil, etc.) and for heating the slop tank. Exhaust gas from the cargo oil pump turbines is introduced into the auxiliary condenser, where a vacuum has been created using an ejector; here seawater cools the steam into drain, which is returned to the cascade tank. The EGE’s superheater cannot be used while the ship is in port, so desuperheated steam is supplied to the turbo generator (T/G). Boiler load increases when cargo handling equipment is in use, so feed water is supplied to the auxiliary boiler using the main feed pump. 2) Boiler water quality management ① Injection of boiler compounds Boiler compounds, diluted with feed water, are injected into the compound tank located along the feed water pipe between the feed water pump and the steam separator drum or auxiliary boiler. Hydrazine, an oxygen scavenger, is diluted in the hydrazine tank using distilled water from the distilled water tank and then injected into the cascade tank using a dedicated pump. ② Water sampling Boiler water samples are taken after the auxiliary boiler water temperature has been lowered using a sample cooler set in the vessel’s work shop. ③ Salinity indicator Salinity indicator cells are located on the outlet-side condensate line for the auxiliary condenser, the atmospheric condenser and the T/G condenser as well as on the air ejector outlet line for the auxiliary condenser. These cells are used to watch for seawater ingress and sound an alarm when salinity levels exceed a permissible range. Marine Boiler Water Management The low-pressure boiler water circulating pump circulates feed water between the exhaust gas economizer (EGE)’s low-pressure steam generator and the steam separator drum while the high-pressure boiler water circulating pump circulates feed water between the EGE’s highpressure steam generator and the auxiliary boiler to generate steam in the steam separator drum and auxiliary boiler, respectively. 019 Chapter 1 ④ Inspection tank An inspection tank is located on this side of the cascade tank on the drain (heated steam, etc.) return line; look inside the tank to check for floating matter (oil content, etc.). ⑤ Blow-off pipe Boiler water inside the steam separator tank and the auxiliary boiler can be drained overboard as necessary to reduce the enrichment of or remove impurities from boiler water. Main boilers (6.0MPaG class) Main boilers for steam turbine ships (double-drum water tube boilers with superheaters) 2-2-3 1) Steam and feed water flow diagram • Steam & Feed Water Flow Diagram for Turbine Ships GLAND STEAM CONDENSATE PUMP H.P. TURBINE MAIN COND. L.P. TURBINE 1ST BLEED (CONDENSATE WATER) P 3RD BLEED B DUMP COND. DESUPERHEATED STEAM DUMP EXT. DSH B STEAM AIR HEATER STEAM DRUM NO.1 DIST. PLANT TO MAIN COND. or DUMP COND. GLAND STEAM SUPER HEATER C MAIN BOILER C STEAM TEMP. CONTROL EXT.DSH. WATER DRUM FROM OTHER BOILER A BOILER COMPOUND TANKS & INJECTION PUMP PUMP TO BOILER STEAM DRUM 3RD.FEED HEATER OVER BOARD CONTINUOUS BOILER WATER MEASURING UNIT C OTHERS ACCOMODATION SC GREASE EXTRACTOR GLAND LEAK 1ST. FEED HEATER GLAND COND. SPILL A TO ATMOS. DRAIN TANK or MAIN COND. CHEMICAL METERING TANK & PUMP SC :SALINITY INDICATOR CELL F.O. TANK HEATING MAKE UP SC P COOLING F.W. CARGO MACHINERY HEATERS P 2ND DEAER. FEED HEATER TO GLAND COND. TO 1ST FEED HEATER or DEAER. F.O. / L.O. HEATERS SHIP SERV. EXT. D.S.H. DRAIN PUMP MAIN FEED PUMP TURNINE TO 1ST FEED HEATER FROM DRAIN TANK ATMOS. DRAIN TANK TO SOOT BLOWERS ECONOMIZER NO.2 DIST. PLANT TO MAIN COND. or DUMP COND. CLEAN DRAIN TURBO GENERATOR SC CONTAMINATED DRAIN TO GLAND COND. TO BURNER ATOMIZER PUMP SC A 2ND BLEED GLAND LEAK SUPERHEATED STEAM Marine Boiler Water Management 020 DISTILLED WATER TANK :CONTROL VALVE DRAIN COOLER DRAIN TANK DE-OILER DRAIN COOLER DE-OILER SAMPLE COOLER TO ATMOS. DRAIN TANK (CLEAN DRAIN) DISTILLED WATER TANK TO ATMOS. DRAIN TANK (CLEAN DRAIN) F.W. TANK DRAIN INSPECT.TANK TO ATMOS. DRAIN TANK (CONTAMINATED DRAIN) OIL CONTENT MONITOR DRINKING WATER TANK (Sterilizer) TO OTHER BOILER STEAM DRUM Fig.12 Marine Boiler Water Management For ships using a steam turbine as the main engine, the plant is operated in a state that resembles a closed feed system; a high vacuum is maintained in the condenser; and dissolved oxygen amounts to 1ppm or less with a similar amount of oxygen dissolved from the atmospheric drain tank. Condensate in the main condenser is pumped by the condensate water pump into the distilling plant, the gland condenser, first feed heater and the second deaerator feed heater (in this order) to be heated. Dissolved oxygen in the feed water is deaerated in the second deaerator feed heater. Feed water is then steam-heated in the third feed heater using the main feed water pump. After the boiler water level has been adjusted by the feed water control valve, the feed water is supplied to the boiler via the economizer. By the time it reaches the boiler inlet, the feed water has been heated to about 200˚C. Some of superheated steam is sent to the steam drum, where it produces the desuperheated steam (approx. 5.85MPaG×320˚C) used for driving the soot blower, heating FO and LO and for cargo machinery heaters. Most of the desuperheated steam then reverts to drain and is recovered in the atmospheric drain tank. Drain recovery rate inside the plant is said to be greater than 99%. The amount of water inside the plant system is controlled by the deaerator feed heater’s water level. If the water level falls, low-salinity (1ppm or less) distilled water produced by the onboard distilling plant is moved from the distilled water tanks (ex. 200m3×2) into the atmospheric drain tank (Make-up). When the water level rises, the surplus is dumped back into the distilled water tanks (Spill). It is customary on board LNG tankers to use the boiler to burn boil-off gas generated in the tanks and seawater-cool the resulting steam into drain. This is done for the purpose of adjusting the internal pressure of the LNG tanks prior to entering port for unloading operations. 021 Marine Boiler Water Management Saturated steam generated in the boiler’s steam drum is transformed into superheated steam (ex. 5.85MPa×525˚C) in the superheater and then used to drive the main turbines (HP and LP), the turbo generator turbine (T/G) and the feed water pump turbine. Exhaust gas that has expanded in the turbine is cooled by seawater in the high-vacuum main condenser; this condensate water (approx. 35˚C) is then used as boiler feed water. Chapter 1 2) Boiler water quality management Marine Boiler Water Management 022 ① Injection of boiler compounds Boiler compounds are dissolved into condensate provided by the condensate system; this mixture is then supplied to the boiler using a dedicated pump. Hydrazine, an oxygen scavenger, is diluted with condensate supplied from the chemical metering tank and then supplied to the line in front of the feed water pump using a dedicated pump. ② Water sampling Boiler water samples taken from the steam drum of each boiler and a feed water sample taken at the third feed heater outlet are cooled with fresh water and automatically monitored by a continuous boiler water measuring instrument. Meanwhile, some items are measured and automatically monitored by a continuous, automatic boiler water analyzer. ③ Salinity indicator Salinity indicators (each one) are located on the outlet-side condensate line for the main condenser pump, on the outlet-side drain line for the dump condenser and atmospheric drain pump, and on the feed water line in front of the feed water pump. They monitor boiler water and sound an alarm if salinity reaches a pre-determined level. Care should be taken regarding the maintenance of salinity indicators. ④ De-oiler and oil content monitor Due to tube damage or for other reasons, oil can find its way into the drain produced from steam that was used to heat fuel oil and lubricating oil. A de-oiler is located in the drain return line to address this problem, removing any oil content that it encounters. In addition, drain exiting the drain cooler in the drain return line is monitored by an oil content monitor, which can detect and determine the concentration of oil content. ⑤ Grease extractor Drain that has returned to the atmospheric drain tank is sent by the drain pump to the feed water line in front of the gland condenser. Since the drain has passed through an open tank, the feed water line is fitted with a grease extractor designed to remove oil content. The grease extractor is subject to periodic inspection and maintenance. ⑥ Blow-off pipe Some boiler water is drained overboard by means of surface blow from the steam drum and bottom blow from the water drum.