Oil-Free Gas Compressors for Liquid Transfer and Vapor Recovery
Blackmer oil-free gas compressors deliver high efficiency in handling propane, butane, anhydrous ammonia and other liquefied gases. They are ideal for rail car unloading and vapor recovery applications. The single-stage, reciprocating compressors are designed to give maximum performance and reliability under the most severe service conditions. All pressure parts are of ductile iron construction for greater resistance to both thermal and mechanical shock. They are designed for ease of maintenance, with all components readily accessible.
Models are available with capacities from 7 to 125 cfm (11.9 to 212 m3/h) with working pressure up to
425 psia (29.31 Bar).
Gas compressors for liquid transfer
Many liquid transfer applications can be handled more efficiently with a gas compressor than a liquid pump. They include unloading of transports and pressure vessels where system piping restricts flow and may cause a pump to cavitate; unloading of LP gas from rail cars, and other installations that require an initial lift to the liquid.
How liquid transfer is accomplished
When transferring liquid, a compressor creates a slight pressure differential between the vessel being unloaded and the receiving tank. The suction stroke of the compressor piston draws in vapor and decreases the receiving tank pressure. The discharge stroke moves a measured volume of vapor at a higher pressure into the supply tank where it displaces an equal volume of liquid through a separate line into the receiving tank. Generally, the liquid flow rate will be 5 to 6 U.S. gpm for each cubic foot (ft3) of piston displacement (670 - 775 liters per cubic meter [m3]).
Gas compressors for vapor recovery
When the liquid transfer phase has been completed, a significant amount of product (vapor and liquid) is left in the tank car (often 3% or more of the tank’s capacity). Recovery of product with a compressor is a simple operation, and thus a compressor can quickly pay for itself.
How vapor recovery is accomplished
Vapor recovery is accomplished with the use of a four-way valve. By rotating the valve handle 90°, gas flow is reversed and the vapor pressure within the supply vessel is reduced. At this point, remaining liquid vaporizes and is quickly recovered. As the tank pressure is drawn down further, remaining vapors are also recovered to an economical level. Recovered vapor is discharged into the liquid area of the receiving tank and then condensed back into a liquid state.
Propane Vapor Recovery
The chart and graph illustrate typical volumes of liquid that may be recovered at various pressures and operating times, based on a 33,000 U.S. water gallon capacity (124,915 liters) tank car – using a Blackmer LB361 gas compressor with 36 CFM (60.3 m3/h piston displacement).
For example, when the liquid transfer phase of unloading is completed, the vapor pressure reads 150 psig (10.34 Bar gauge). At this condition, there would be approximately 1,315 U.S. gallons (4,978 liters) of LP gas in vapor form remaining in the tank car. Of this amount, 845 U.S. gallons (3,199 liters) can be economically recovered in less than three hours.
1 Physical properties are based on N.F.P.A. 58 data for commercial propane. Vapor pressure 205 psig (14.13 Bar) @ 100ºF (37.8ºC).
2 Economically recoverable product is based on reduction of tank pressure to 25% of original value. Residual liquid not included.
Note: A different size tank will have a proportional relationship to the values shown above. For example, a 10,000 U.S. gallon
(27,850 liters) tank would represent 30.3% of the values given.
Volume Recovered From 33,000 U.S. Gallon Tank (124,915 Liters)
Overall efficiency of plant piping may improve or detrimentally affect
compressor performance.
All figures are approximate and rounded off for easy reading.
Additional information for liquefied gases other than propane is
available: consult your Blackmer representative.
Design Features
1. High efficiency valves move more gas volume
The heart of any compressor is its valve assembly and Blackmer valves are specifically designed for non-lubricated gas applications. With precisely engineered clearances, spring tension, and a special finish, these valves seat more positively so more gas is moved with each piston stroke. Blackmer valves offer greater strength, quiet operation, and long life.
2. O-Ring seals - head and cylinder
The head and cylinder are sealed with O-rings to ensure positive sealing under all operating conditions.
3. Pressure assisted piston rings for positive seating
Constructed of self-lubricating PTFE, Blackmer’s special ring design provides maximum sealing efficiency with minimal friction wear. The result: peak performance and extended compressor service life.
4. Heavy-duty crankshaft
The ductile iron crankshaft is precision ground with integral counterweights for smooth, quiet operation. Rifle drilling ensures positive oil distribution to the wrist pin and connecting rod bearings.
5. Pressure lubricated crankcase
A rotary oil pump provides positive oil distribution to all running gear components for long life and minimal wear.
6. Ductile iron pistons
Heavy-duty ductile iron pistons are connected with a single positive locking nut which eliminates potential problems associated with more complex designs.
7. Self-adjusting piston rod seals
Crankcase oil contamination and cylinder blow-by is prevented with loaded glass-filled PTFE seals which maintain a constant sealing pressure around the piston rods.
8. Ductile iron construction
All pressure parts are of ductile iron for greater resistance to both thermal and mechanical shock.
9. Wear-resistant crosshead assemblies
Designed for maximum lubrication and wear resistance.
Compressor Selection Data
To select a compressor that best fits your application requirements, use the charts shown. The data provided is based on approximate delivery rates when handling propane or anhydrous ammonia. Actual capacities will depend upon line restrictions, size and length of piping. Horsepower requirements for both liquid transfer and vapor recovery applications are based on moderate climatic conditions.
Engineering Specifications
* Double acting
1 Compression Ratio defined as absolute discharge pressure divided by
absolute inlet pressure.
2 Compression Ratios are limited by discharge temperature. High compression
ratios can create excessive heat, i.e., over 350ºF (117ºC). The duty cycle must
provide for adequate cooling time between periods of operation to prevent
excessive operating temperature.
Compressor Selection Data: Propane and Anhydrous Ammonia
click table to see larger
* Maximum rpm for each respective motor horsepower.
1 Delivery will depend on proper system design, pipe sizing and valve capacity.
2 Horsepower is for liquid transfer and vapor recovery in moderate climates. For liquid transfer without vapor recovery, horsepower will be lower. For severe climates, contact your
Blackmer representative for horsepower required.
3 Use next larger pipe size if piping exceeds 100 feet (30 meters).
Standard Compressor Packages
Blackmer offers a variety of factory assembled compressor packages to fit most application requirements. Standard base mounted units are available in the following styles:
CO - COMPRESSOR ONLY Includes basic compressor with flywheel.
B - BASE MOUNTED UNIT Includes compressor, pressure gauges, formed steel base, V-belt drive with belt guard, and adjustable motor base, less motor.
E - EXTENDED SHAFT Includes compressor with flywheel and extended crankshaft.
TU - TRANSFER UNIT Includes compressor, pressure gauges, formed steel base, liquid trap assembly with a mechanical float, V-belt drive with belt guard, and adjustable motor base, less motor.
TC or TW - TRANSFER UNIT Includes compressor, pressure gauges, formed steel base, ASME code stamped liquid trap assembly (complete with relief valve and a NEMA 7 electric float switch for Propane service), V-belt drive with belt guard, and adjustable motor slide base.
LU - LIQUID TRANSFER/VAPOR RECOVERY UNIT Includes compressor, pressure gauges, formed steel base, liquid trap assembly with a mechanical float, inlet strainer, interconnecting piping, 4-way valve, V-belt drive with belt guard, and adjustable motor base, less motor.
LC or LW - LIQUID TRANSFER/VAPOR RECOVERY UNIT Includes compressor, pressure gauges, steel base, ASME code stamped liquid trap assembly (complete with relief valve and a NEMA 7 electric float switch for Propane service), inlet strainer, interconnecting piping, 4-way valve, V-belt drive with belt guard, and adjustable motor base, less motor.
All Compressor models are available with or without motors or accessories. Special engine drives, control panels and custom emergency evacuation units can be furnished on a special order basis.
Blackmer compressors can also be mounted on transports with direct drive or V-belt drive, as shown below.
Multiple Seal Options
For applications that require maximum leakage control, double piston rod seals and a distance piece chamber are available for all Blackmer LB compressors. Blackmer also offers a line of singe and two-stage industrial gas compressors with double or triple piston rod seals and air or water cooling. Consult your Blackmer representative for more information and specifications.
Optional Accessories
Motors: Standard voltage and sizes in stock.
Motor slide rails: Offer easy adjustment for standard motor frame sizes.
Engines: Diesel, propane or gasoline fueled engines available.
Liquid traps: Standard liquid traps have a mechanical float to protect the compressor by preventing liquid from entering. These traps may be fitted with an electric float switch to sound an alarm or stop the compressor in the event of high liquid level. Larger traps with ASME code construction and one or two electric float switches are also available.
Vapor strainer assembly: Features a 30-mesh replaceable stainless steel screen and ductile iron body.
Four-way valve: Four-way valves allow easy switching from liquid transfer to vapor recovery operation by reversing the system flow direction. Standard valves are ductile iron with a handle and easy-to-read flow direction indicator. Valves with electric or pneumatic actuation are available if remote operation is desired.
Pressure gauges: Standard 1?4-inch NPT liquid-filled for head mounting.
Extended crankshaft: For direct drive mounting, or V-belt drive applications.
Base plates: Formed steel or fabricated skid type.
Belt guards: Heavy-duty 14-gauge steel, stainless steel or non-sparking aluminum construction.
Custom engineered LPG transfer compressor package