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3.4.6 Student Book © 2004 Propane Education & Research CouncilPage 1 3.4.6 Maintaining Bulk Plant Compressors Knowledge of the processes involved in maintaining.

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Presentation on theme: "3.4.6 Student Book © 2004 Propane Education & Research CouncilPage 1 3.4.6 Maintaining Bulk Plant Compressors Knowledge of the processes involved in maintaining."— Presentation transcript:

1 3.4.6 Student Book © 2004 Propane Education & Research CouncilPage Maintaining Bulk Plant Compressors Knowledge of the processes involved in maintaining bulk plant compressors is necessary for safe and efficient plant operations. In this module you will learn to identify: (1)Devices basic to compressor operations (2)Compressor protective devices (3)Basic compressor operations (4)Procedures for maintaining compressor systems

2 3.4.6 Student Book © 2004 Propane Education & Research CouncilPage 1 Devices Basic to Compressor Operations Propane compressors transfer liquid from one container to another by creating a [vapor] pressure difference between the supply tank and the receiver tank. Figure 1. Transferring Propane with a Compressor

3 3.4.6 Student Book © 2004 Propane Education & Research CouncilPage 2 Devices Basic to Compressor Operations The ratio between the absolute intake and absolute exhaust pressure is known as the compression ratio and is usually monitored by means of pressure gauges mounted in the inlet and outlet connections to the compressor. Figure 2. Propane Compressor

4 3.4.6 Student Book © 2004 Propane Education & Research CouncilPages 2 & 3 Devices Basic to Compressor Operations Valve Assemblies— Most compressors are designed so the valves can be easily removed for inspection. If found to be worn or damaged, they are usually replaced as an assembly and not rebuilt. Piston, Crosshead and Packing Seal— Many propane compressors are "oil-less" or "dry" compressors, especially designed to prevent the oil they use for lubrication from being compressed along with the vapor in the compression chamber. Lubrication System— At the bottom of the compressor is a sump that contains the compressor's oil supply and an oil pump or slinger.

5 3.4.6 Student Book © 2004 Propane Education & Research CouncilPages 3 & 4 Devices Basic to Compressor Operations Cooling System— A fan built into the flywheel at the rear of the compressor cools the fins by blowing air across them whenever the compressor is running. Compressors should never be mounted closer than 18 inches to a wall or other surface that would restrict free movement of air and should always be 18 inches above grade to prevent the flywheel fan from blowing dirt and debris into cooling fins. Drive System — Stationary compressors are usually driven by explosion-proof electrical motors attached to the compressor drive shaft with V-belts and pulleys.

6 3.4.6 Student Book © 2004 Propane Education & Research CouncilPage 5 Identifying Basic Compressor Protective Devices Figure 4. Compressor System with Protective Line Devices

7 3.4.6 Student Book © 2004 Propane Education & Research CouncilPages 5 & 6 Identifying Basic Compressor Protective Devices Strainer— Compressors can be damaged by dirt, pipe scale, and other debris in the plant piping system. Strainers are usually ordered according to the pipe size and their inlet and outlet openings and are usually at least one pipe size larger than the system vapor piping to minimize restrictions to flow. Liquid Trap— To prevent liquid from reaching the compression chamber, most compressors have a liquid trap installed in the inlet piping between the strainer and the compressor intake.

8 3.4.6 Student Book © 2004 Propane Education & Research CouncilPage 6 Identifying Basic Compressor Protective Devices Liquid Trap Figure 5. Liquid Trap

9 3.4.6 Student Book © 2004 Propane Education & Research CouncilPage 7 Identifying Basic Compressor Protective Devices Discharge Relief Valve— Compressor systems must be protected against damage from excessively high pressure. For this reason, the discharge line of most compressors is equipped with a discharge relief valve. Discharge valves should be inspected regularly for leaks and to be sure the inside of the valve is free from corrosion and accumulations of debris that would prevent the valve from opening and closing properly. CAUTION: When inspecting relief valves, use an inspection mirror or similar device to check inside of the valve. Never look directly into the outlet of any valve.

10 3.4.6 Student Book © 2004 Propane Education & Research CouncilPages 7 & 8 Identifying Basic Compressor Operations Compressor operations are usually used in unloading operations. Vapor Recovery Operations Even when a tank appears to be empty of liquid, it is full of propane vapor. The tank may also contain some liquid (called a "liquid heel") which lies too low in the tank to be accessible from the liquid withdrawal connection. While such small amounts of the product may seem insignificant, they are not. For example, an "empty" jumbo railcar may actually contain enough vapor to make nearly 1,500 gallons of propane liquid. For obvious reasons then, many dealers find it worthwhile to recover some of the propane vapor left in railcars and other large tanks. The compressor withdraws vapor from the tank car and forces it into the liquid space of the plant storage tank, where the cooler temperature condenses the vapor back into a liquid. The compressor is actually lowering the pressure in the tank car by withdrawing vapor, the compressor also removes the liquid heel, which boils off with the drop in pressure.

11 3.4.6 Student Book © 2004 Propane Education & Research CouncilPage 8 Identifying Basic Compressor Operations Figure 6. Three Valve Manifold Piping System Courtesy of Corken, Inc.

12 3.4.6 Student Book © 2004 Propane Education & Research CouncilPage 9 Identifying Basic Compressor Operations Some installations stop vapor recovery operations when the inlet pressure at the compressor reaches some predetermined value. This value is usually somewhere between 30 and 50 psig. Others stop when the ratio between the inlet and outlet pressures become approximately one-to-four. Figure 7. Vapor Recovery Graph PROPANE EVACUATION TIME for 33,000 Gallon W.C. (124,905 Liter) Capacity Railcar (Model "B" Size Compressor)

13 3.4.6 Student Book © 2004 Propane Education & Research CouncilPages 9 & 10 Identifying Basic Compressor Operations Piping Manifolds and Piping Systems The compressor is always installed together with a piping manifold, which is located near the compressor and used to control the flow of vapor through the system during transfer operations. The exact construction of the manifold depends upon the types of operations for which the compressor will be used. The size of the vapor and liquid piping, which must be large enough to deliver the rated flow capacity of the compressor is very important. Undersized piping will result in high differential pressures, lower flow rates, and increased horsepower requirements for the compressor drive system. The compressor should be located as close as practicable to the tank to be unloaded.

14 3.4.6 Student Book © 2004 Propane Education & Research CouncilPage 10 Identifying Basic Compressor Operations Four-Way Directional Control Valves Figure 8. Four-Way Directional Control Valve

15 3.4.6 Student Book © 2004 Propane Education & Research CouncilPage 11 Compressor System Maintenance Procedures Drive System Maintenance — Check V-belts daily for proper alignment and tension. Like the V-belts on pump drive systems, they should depress 1/2" to 3/4" under moderate thumb pressure. Lubrication System Maintenance — Check the crankcase for leaks, especially around the flywheel-end of the crankshaft, the dipstick, and the breather valve assembly. When checking the breather valve assembly, be sure that it is clear and free of any dirt or trash. Check the oil level in the crankcase. If the oil level is low, check the manufacturer's instructions for the type of oil to use and the amount to add. Check the oil pressure gauge. If the oil pressure is unusually high or low, shut down the compressor.

16 3.4.6 Student Book © 2004 Propane Education & Research CouncilPages 11 & 12 Compressor System Maintenance Procedures Packing Maintenance — Check the packings for leaks on a daily basis. Liquid Trap Assembly

17 3.4.6 Student Book © 2004 Propane Education & Research CouncilPages Time to See If You Got the Key Points of This Module… Complete the Review on pages 13 & 14. See if you are ready for the Certification Exam by checking off the performance criteria on pages 15 & 16.


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