Loading and unloading compressor

This series of oil-free lubricating compressors is one of the first products produced by our factory in China. The product has the characteristics of low speed, high component strength, stable operation, long service life and convenient maintenance. Among them, the ZW series compressors are in the form of units. It integrates compressor, gas-liquid separator, filter, two-position four-way valve, safety valve, check valve, explosion-proof motor and chassis as a whole. It has the characteristics of small size, light weight, low noise, good sealing, easy installation and easy operation.

This product is mainly used for unloading, loading, tank dumping, residual gas recovery and residual liquid recovery of LPG/C4, propylene and liquid ammonia. Widely used in gas, chemical, energy and other industries, it is the key equipment for gas, chemical, energy and other industries.

Note: During the unloading process, the compressor pressurizes the gas from the storage tank and then presses it into the tanker through the gas phase pipeline, and the liquid is pressed from the tanker to the storage tank through the pressure difference of the gas phase to complete the unloading process. When the gas phase is pressurized, the temperature of the gas phase will rise. At this time, it is not necessary to forcibly cool it, because if the gas phase is compressed and then cooled, it is easy to liquefy, and it is difficult to establish the pressure difference of the gas phase, which is not conducive to the replacement of the gas phase and the liquid phase. In short, it will cause the extension of the unloading process time. If residual gas recovery is required, the cooler can be selected to forcibly cool the gas phase during residual gas recovery operation, so as to recover residual gas as soon as possible.

The loading process is the opposite of the unloading process.

The unloading volume is calculated based on inlet pressure 1.0MPa, exhaust pressure 1.6MPa, inlet temperature 40°C, and liquefied gas liquid density 582.5kg/m3. When the working conditions change, the unloading volume will change accordingly, for reference only.

Suction pressure: ≤1.6MPa

Exhaust pressure: ≤2.4MPa

Maximum pressure difference: 0.8MPa

Maximum instantaneous pressure ratio: ≤4

Cooling method: air cooling

The unloading capacity is calculated based on inlet pressure 1.6MPa, exhaust pressure 2.4MPa, inlet temperature 40°C, and propylene liquid density 614kg/m3. When the working conditions change, the unloading capacity will change accordingly, for reference only.

Suction pressure: ≤1.6MPa

Exhaust pressure: ≤2.4MPa

Maximum pressure difference: 0.8MPa

Maximum instantaneous pressure ratio: ≤4

Cooling method: air cooling

The unloading capacity is calculated based on inlet pressure 1.6MPa, exhaust pressure 2.4MPa, inlet temperature 40°C, and liquid ammonia liquid density 729kg/m3. When the working conditions change, the unloading capacity will change accordingly, for reference only.

Schematic diagram of unloading process

Open the liquid phase pipe between the tanker and the storage tank at the beginning of liquid delivery. If the liquid level in the tanker is higher than the storage tank, it will automatically flow into the storage tank. When the balance is reached, the flow will stop. If the liquid phase of the tank car is lower than the storage tank, start the compressor directly, and the four-way valve is in the positive position, and the gas is extracted from the storage tank through the compressor to pressurize and then discharged into the tank car. At this time, the pressure in the tank car rises, the pressure in the storage tank drops, and the liquid in the tank car flows into the storage tank. (As shown  below)

Residual liquid recovery

The remaining liquid recovery process is the opposite of liquid delivery. After the liquid is conveyed, the four-way valve should be reversed, and the dotted pipeline in the figure is closed. At this time, the remaining gas in the tank car is inhaled by the compressor, pressurized and discharged to the storage tank until the pressure of the remaining gas drops to no recovery value. When recovering, pay attention to the compressor pressure ratio and exhaust temperature not exceeding the allowable value.

Four-way valve working principle

 Pull the handle of the four-way valve, when the four-way valve is in the position shown in Figure a, the A end is the intake air, and the gas flows from A to B, passing through the connecting pipe, intake filter parts, compressor intake pipe, compressor, Compressor exhaust pipe, D end flows to C end, and C end is the exhaust end.

When the four-way valve is in the position B in the figure, the C terminal is the intake air, and the gas flows from the C terminal to the B terminal, through the connection pipe, the intake filter part, the compressor intake pipe, the compressor, the compressor exhaust pipe, and the D terminal It flows to the A side, and the A side is the exhaust side.

Calculation Reference Example of Type Selection and Calculation of Liquid Ammonia Unloading Compressor

一、Compressor inlet and outlet pressure selection

The saturated vapor pressure of liquid ammonia at 20~36°C

In the case of high temperature, the saturated vapor pressure of liquid ammonia is high, so the 16 (intake pressure)-24 (exhaust pressure) model is selected to meet the high temperature use environment.

Note: The pressure unit is kg/cm2

二、Compressor Displacement Calculation

The calculation of the specific flow rate is more complicated, and it needs to be finally determined according to the calculation formula and experience. Only a simple calculation method is introduced here.

1. Calculate the volume of the tank car

According to the provided working conditions, first determine the total volume flow required to unload 15 tons of liquid ammonia tanker in one hour.

The specific gravity of liquid ammonia is 0.618, so the volume of 15 tons of liquid ammonia is: 15 ÷ 0.618 = 24.272m3; and since the tank truck is not allowed to be filled up, it is generally filled to about 80% of the volume of the tank truck, then the tank truck The volume is 24.272+15×0.2=27.272, so the volume of the tank car should be 30m3.

2. Calculate displacement

When the compressor is unloading, the pressure difference must first be established before the liquefied ammonia can be unloaded from the tanker to the storage tank. Generally, the time for establishing the pressure difference is 15 minutes, so the actual unloading time is only about 45 minutes, which is the required displacement. It is 30÷45＝0.66667m3/min; and after the gas is pressurized from 16kg to 24kg by the compressor, the volume will be reduced to about 0.66667 (16÷24) of the original volume, and the displacement of the compressor is: 0.66667÷0.66667＝ 1m3/min

According to the above calculation, the compressor model is selected as ZW-1.1/16-24