A Guide to Selecting the Correct Gas Booster

Parameters Required

The answers to the following questions will provide the parameters for the selection of any gas booster or ProPak booster system.

1. What is the maximum pressure to be attained?

You need to know the pressure that the system will have to reach, either now or sometime in the future. This does not need to be the usual working pressure, but the maximum pressure ever needed.

2. What is the required flow rate?

You need to know the required flow rate at the required discharge pressure. This is not the flow rate at the maximum pressure, but the flow rate at the working pressure. Remember that every booster has a maximum pressure where it will stall and produce no flow, but at any pressure less than that it will produce flow. This flow reduces in quantity as the output pressure approaches the stall pressure.

3. Is the flow rate constant?

Do you have a process application where you need a constant flow at a constant pressure? If so, then this is expressed as “x” SCFM (NM3) @ “y” PSIG (Barg).

4. Is the flow rate decreasing?

Do you have an application where you are filling cylinders or some other vessel from a lower supply pressure to a higher storage pressure. To select the proper booster or booster system, you need to know the size of the vessel to be filled. This can be supplied in any form that can be converted to ACF.

5. What is the required fill time for the vessel?

It is very common to have an initial fill times that is unrealistic. Many people who are not
familiar with gases ask for fill times that will require uneconomic systems. Therefore it is important to think about the longest possible fill time the application can stand.

6. What is the gas supply pressure?

The performance of any gas booster is a function of the incoming gas pressure. Simply stated: “any gas booster will only discharge the amount of gas it takes in”. The higher the inlet gas pressure, the more SCF of gas are squeezed into the gas section and
therefore the more gas discharged. Gas supply can have more than one source. Therefore it can have many combinations of flow, pressure and temperature.

7. What is the drive pressure?

This is not the initial pressure in the system first thing in the morning before all of the uses of air are operational, but rather should be the minimum that the plant experiences throughout the day. The booster may have to provide maximum performance when the drive conditions are at their worst.

8. What is the gas?

Some gases cannot be pumped with standard boosters. They may require special seals, materials of construction, venting and other considerations. This is also important when higher pressures are required in filling applications to determine the compressibility of the gas. Applications involving gas boosters will always fall into one of four categories. It is very important to clearly determine into which category a particular application fits.

a) The supply pressure is at a constant pressure (Ps) and the discharge gas is at a constant flow (Q) and pressure (Po).

b) The supply gas is from a decreasing pressure and the discharge gas is at a constant flow and pressure. It is safe to assume that the supply flow rate will decrease as the supply pressure decreases. To maintain the constant outlet flow the booster will have to increase its cycle rate.

c) The supply gas is at a constant flow and pressure and the discharge gas it at an increasing 8 pressure.. It is safe to assume that the discharge flow rate will decrease as the discharge
pressure Increases.

d) The supply gas is at a decreasing pressure and the discharge gas is at an increasing pressure. It is safe to assume that the flow rate will decrease significantly as the pressures get further apart.

Steps

Step 1.

Determine the area ratio required – Outlet pressure divided by air drive pressure

Step 2.

Determine compression ratio required. – Outlet pressure divided by inlet pressure (lowest)

Step 3.

Determine the number of stages required. A 6:1 Compression Ratio between stages is a good aim

Step 4.

Establish model number whose last stage exceeds the area ratio requirements ascertained in step 1.

Step 5.

In the case of 2 stage units, select the model whose first stage can accept the supply gas parameters. This is where interstage stall can be an issue on 2 stage boosters

Step 6.

Use performance curves to select the best model for the application