Filtration Systems: Maintenance & Troubleshooting

• The lesson covers types of filters, basic maintenance, changeover decisions, troubleshooting, LOTO preparation, and safety during changeover.

Process Symbols

• Symbols relating to filters and their auxiliary components
• Differential Pressure (DP) is a key measurement
• Bypass lines allow flow to circumvent the filter
• Pressure Gauges (PG) are used to measure pressure
• Pressure Relief Valves are important safety components

Introduction to Filtration

• Filtration separates different phases of a mixture
• A filter medium is a porous barrier used to separate solid particles or contaminants from liquids or gases
• The filter medium provides resistance during filtration, which remains constant unless solid particles penetrate it
• Filter cake refers to solid particles that deposit on the filter medium

Filtration Terminology

• Filtrate refers to the liquid that passes through the filter medium
• A filter bed equals filter cake plus filter medium
• The filter bed gives resistance to flow

Types of Filters

• There are three types of filters: cake filter, depth filter, and surface filter

Cake Filters

• Characterized by porous filter media with small openings
• Particulates are retained on the surface, while liquids pass through
• Filter material can be wire mesh, cloth, paper, or engineering material
• Bag filters are cake filters used for dust removal

Depth Filters

• Used to pass liquids containing suspended solids through a sand filter
• Suspended solids are caught in the spaces between sand particles
• Reduced open space causes high pressure drop, and the filter requires regeneration
• Filter medium used in sand filters is sand
• Sand filters need little maintenance, and use gravity and pressure as driving forces

Cartridge Filters

• A type of depth filter made of synthetic fibers, paper, or metal
• Cartridge filters have different opening sizes
• Filtration flow happens from outside to the center

Surface Filters

• Have a uniform opening size
• Strainers, gratings, and membranes are typical examples
• The surface filter can be washed after clogging
• Used in water treatment, reservoirs, or drains to get rid of large solid particles like tree branches and debris

Y-Strainers

• A Y-strainer can clog and affect suction flow to the pump
• Also used in wastewater systems for visible solids removal
• Y-strainers are used in piping systems to safeguard pumps and compressors

Membrane Filters

• Classified three ways
• Porous: hole diameter in the range of 0.005 - 1 micron
• Microspores have a hole diameter in the range of 0.001 - 0.005 micron
• Non-porous filters contain a hole diameter smaller than .001 micron

Membrane Filters in Industry

• Membrane: thin, man-made material with small pores, used to separate dissolved substances from solutions via reverse osmosis
• Filtrate is pressure driven to separate dissolve salts
• Membrane filters are expensive and used in specialized industries
• Ultra-pure water production for semiconductor plants and pharmaceutical sectors
• Drinking water production in new water plants
• Separating/concentrating dairy in the food industry
• Recovering paint in paint industries

Filter Applications - Type and Size

• Gratings, a surface filter, can remove 10-1cm size debris
• Screens/strainers are surface filters that trap smaller particles like visible solids (0.1 mm - 1 cm)
• Sand filters are depth filters that help trap particles approximately 25 micron in size, like water treatment
• Bag filters are cake filters and trap 200-1micron dust

Filter Applications - Industry Usage

• Cartridge filters, a depth filter, help purify/contaminant levels less then 0.01%
• Membrane filters, a surface filter, help dairy, chemical and pharmaceutical industries
• Membrane filters help purify water, separate products and help remove particles

Filter Operation

• Pressure drop across porous media rises with fluid viscosity, cake thickness, and liquid flow rate causing the need for maintenance
• Backflushing, filter replacement, or filtrate drainage can address high pressure drops

Operational Steps

• The filter should be equipped with pressure gauges, drain and vent points, a pressure relief valve, and a standby filter
• Line up the low-pressure side (outlet) and high-pressure side (inlet) during filter operation
• Changeover of on-going filter happens when servicing is needed
• Calculate the pressure drop for clogged filters to improve performance

Changeover Overview

• The changeover process ensures continued operation by switching from a faulty filter to a standby filter

Problem Identification

• Involves identifying the problem and its symptoms
• Symptoms include process variables outside normal range
• When an alarm triggers that is out of the ordinary
• When the process is shut down automatically
• Unusual pressure or flow rates in the filter line

Determining the Cause

• Involves asking whether changes are abrupt or gradual, whether it is intermittent, if this happened before and under what condition
• One useful method is the process of elimination, with four methodologies: Input/Output, Bracketing, Serial, and Half-splitting

Cause Determination Methodologies- I/O Method

• Input/Output Method requires familiarity with normal process variable values
• How to apply: If inlet temperature is normal but the outlet temperature is abnormal, there is likely a problem

Cause Determination Methodologies- Bracketing

• Bracketing method narrows the problem to a specific process
• Two identical train processes transfer to a product tank, where the final product is determined to be off-spec.
• If the final product leaving one train is on-spec, the other train must be off-spec

Cause Determination Methodologies- Serial

• The serial method is logical and effective but very time-consuming
• Water contaminated the final product after possibly entering in the steam heater, reactor, reboiler, condenser and product cooler.
• Taking samples at different point helps tell if there is a presence of water

Cause Determination Methodologies- Half-Splitting

• Half splitting: split the process in half to reduce possible causes quickly
• The control system includes a transmitter, controller, I/P converter, and control valve.
• Test the output signal from the controller to see if the signal and the transmitter match

Changeover Procedures

• Includes lining up to the bypass line or standby filter, isolating the high-pressure side (inlet) and low-pressure side of the filter

Preparing for Maintenance with LOTO

• Lock out tag out (LOTO): mechanical device to prevent fluid/gas transfer in piping
• LOTO prevents accidental mixing, unauthorized valve operation, and endangering repair staff Isolating devices include gate/globe valve, ball valve, butterfly valve , and blinds

Maintenance Considerations

• Precaution includes isolation and depressurization before replacement
• Isolation: close all interconnected valves to reduce pressure
• Depressurizing: reduce system pressure to prepare for liquid drainage and purging

Safety Precautions

• Identify any hazardous chemicals used
• The area should be clean, clear, and equipped with fire extinguishers
• Ensure light hydrocarbons do not accumulate in trenches
• Watch for any leaks, and do not block anything

Changeover Safety

• Depressurize and drain light hydrocarbon liquid, releasing area if need be
• Detonating vapor forms when hydrocarbon mixes with air so ensure no air enters
• Equipment replaced after maintenance gets air/gas freeing before putting into standby/Ensuring the standby equipment is not over pressure

Learn about different types of filters and their maintenance. Understand changeover decisions and troubleshooting techniques. Explore Lockout/Tagout (LOTO) preparation and safety measures during filter changeovers, including process symbols, filtration terminology, and filter components.