# Designing a Gas Collection System

In this example we are not concerned with building the model and data entry. Instead we focus on the engineering. Problem Statement: It is desired to collect together the air vents from a group of 5 storage tanks holding a flammable, obnoxious liquid. The vent gas is to be treated in an activated carbon bed before finally passing to atmosphere. In this problem we are only concerned with the situation that occurs as the tanks are filling. In our scenario each tank vents gas (for simplicity considered to be air), at the rate of which it can be filled. The exit gas vent from each tank is modeled as a known flow element, with the maximum tank fill rates already entered. The remainder of the collection network has been built and can be opened from "[FluidFlow3 folder]\Examples\Non Sized Gas Collection System.ff3". Open the example and consider how we may answer the following question. 1. Size all pipes so that the operating pressure under maximum filling rates does not exceed that allowed under code API 650. This means no more than 1 psig operating pressure in each storage tank. Considerations and approach: We will take the worst case of all 5 tanks filling at one time. To easily view the calculation result values we can use one of three possible techniques: ▪We can configure and turn on the fly by results. In this way we can move the mouse over the flowsheet and look at the result values we are interested in. ▪We can click the Results tab in the data palette on the left click on the flowsheet to select each component we are interested in. ▪We can show the results on the flowsheet. It is important to state at the outset that there are many solutions to this problem. For example we could increase all line sizes until the pressure in each tank dropped below 1 psig. This would undoubtedly work, but as the lines are made of stainless steel and are of a reasonable length we may not wish to over design in this way due to cost considerations. To start, let us consider the tank pressures if we use 2" pipe throughout (this is the case if we open the example). You can see that each tank is over the maximum allowed pressure of 1 psig. Click on any pipe and look at the results table in the data palette. You can see immediately that each pipe is already larger than the size recommended according to the economic size. This is an important point and illustrates that you cannot blindly set all pipe sizes to the suggested economic size in all cases. Click on a few more components and consider the row titled "Non Recoverable Loss", this loss represents the pressure loss that can never be recovered. It is this value that we must impact (reduce) if we are to design a safe system. You should quickly note that the majority of the system pressure loss occurs at the packed bed. The packed bed represents a pressure loss of 0.6 psi out of a total of < 1psi available. Using this knowledge, perhaps the best approach to take is to increase the diameter of the bed to reduce the pressure loss, rather than increase the pipe size of each pipe. This now becomes a cost issue. For example is it less expensive to change the diameter of the bed, or use a different particle size in the bed rather than change the pipe sizes. We do not have sufficient information to fully consider the available choices. What is important is that you recognise how to utilize the power of FluidFlow to consider the alternative design scenarios. If you have the scripting module you can automate this process. An acceptable design changing only pipe sizes downstream of the Tee junction (node 15) is saved as "Pipe Sized Gas Collection System".In this example we are not concerned with building the model and data entry. Instead we focus on the engineering. Problem Statement: It is desired to collect together the air vents from a group of 5 storage tanks holding a flammable, obnoxious liquid. The vent gas is to be treated in an activated carbon bed before finally passing to atmosphere. In this problem we are only concerned with the situation that occurs as the tanks are filling. In our scenario each tank vents gas (for simplicity considered to be air), at the rate of which it can be filled. The exit gas vent from each tank is modeled as a known flow element, with the maximum tank fill rates already entered. The remainder of the collection network has been built and can be opened from "[FluidFlow3 folder]\Examples\Non Sized Gas Collection System.ff3". Open the example and consider how we may answer the following question. 1. Size all pipes so that the operating pressure under maximum filling rates does not exceed that allowed under code API 650. This means no more than 1 psig operating pressure in each storage tank. Considerations and approach: We will take the worst case of all 5 tanks filling at one time. To easily view the calculation result values we can use one of three possible techniques: ▪We can configure and turn on the fly by results. In this way we can move the mouse over the flowsheet and look at the result values we are interested in. ▪We can click the Results tab in the data palette on the left click on the flowsheet to select each component we are interested in. ▪We can show the results on the flowsheet. It is important to state at the outset that there are many solutions to this problem. For example we could increase all line sizes until the pressure in each tank dropped below 1 psig. This would undoubtedly work, but as the lines are made of stainless steel and are of a reasonable length we may not wish to over design in this way due to cost considerations. To start, let us consider the tank pressures if we use 2" pipe throughout (this is the case if we open the example). You can see that each tank is over the maximum allowed pressure of 1 psig. Click on any pipe and look at the results table in the data palette. You can see immediately that each pipe is already larger than the size recommended according to the economic size. This is an important point and illustrates that you cannot blindly set all pipe sizes to the suggested economic size in all cases. Click on a few more components and consider the row titled "Non Recoverable Loss", this loss represents the pressure loss that can never be recovered. It is this value that we must impact (reduce) if we are to design a safe system. You should quickly note that the majority of the system pressure loss occurs at the packed bed. The packed bed represents a pressure loss of 0.6 psi out of a total of < 1psi available. Using this knowledge, perhaps the best approach to take is to increase the diameter of the bed to reduce the pressure loss, rather than increase the pipe size of each pipe. This now becomes a cost issue. For example is it less expensive to change the diameter of the bed, or use a different particle size in the bed rather than change the pipe sizes. We do not have sufficient information to fully consider the available choices. What is important is that you recognise how to utilize the power of FluidFlow to consider the alternative design scenarios. If you have the scripting module you can automate this process. An acceptable design changing only pipe sizes downstream of the Tee junction (node 15) is saved as "Pipe Sized Gas Collection System". In this example we are not concerned with building the model and data entry. Instead we focus on the engineering. Problem Statement: It is desired to collect together the air vents from a group of 5 storage tanks holding a flammable, obnoxious liquid. The vent gas is to be treated in an activated carbon bed before finally passing to atmosphere. In this problem we are only concerned with the situation that occurs as the tanks are filling. In our scenario each tank vents gas (for simplicity considered to be air), at the rate of which it can be filled. The exit gas vent from each tank is modeled as a known flow element, with the maximum tank fill rates already entered. The remainder of the collection network has been built and can be opened from "[FluidFlow3 folder]\Examples\Non Sized Gas Collection System.ff3". Open the example and consider how we may answer the following question. 1. Size all pipes so that the operating pressure under maximum filling rates does not exceed that allowed under code API 650. This means no more than 1 psig operating pressure in each storage tank. Considerations and approach: We will take the worst case of all 5 tanks filling at one time. To easily view the calculation result values we can use one of three possible techniques: ▪We can configure and turn on the fly by results. In this way we can move the mouse over the flowsheet and look at the result values we are interested in. ▪We can click the Results tab in the data palette on the left click on the flowsheet to select each component we are interested in. ▪We can show the results on the flowsheet. It is important to state at the outset that there are many solutions to this problem. For example we could increase all line sizes until the pressure in each tank dropped below 1 psig. This would undoubtedly work, but as the lines are made of stainless steel and are of a reasonable length we may not wish to over design in this way due to cost considerations. To start, let us consider the tank pressures if we use 2" pipe throughout (this is the case if we open the example). You can see that each tank is over the maximum allowed pressure of 1 psig. Click on any pipe and look at the results table in the data palette. You can see immediately that each pipe is already larger than the size recommended according to the economic size. This is an important point and illustrates that you cannot blindly set all pipe sizes to the suggested economic size in all cases. Click on a few more components and consider the row titled "Non Recoverable Loss", this loss represents the pressure loss that can never be recovered. It is this value that we must impact (reduce) if we are to design a safe system. You should quickly note that the majority of the system pressure loss occurs at the packed bed. The packed bed represents a pressure loss of 0.6 psi out of a total of < 1 psi available. Using this knowledge, perhaps the best approach to take is to increase the diameter of the bed to reduce the pressure loss, rather than increase the pipe size of each pipe. This now becomes a cost issue. For example is it less expensive to change the diameter of the bed, or use a different particle size in the bed rather than change the pipe sizes. We do not have sufficient information to fully consider the available choices. What is important is that you recognize how to utilize the power of FluidFlow to consider the alternative design scenarios. If you have the scripting module you can automate this process. An acceptable design changing only pipe sizes downstream of the Tee junction (node 15) is saved as "Pipe Sized Gas Collection System".