6 replies to this topic

[yeek]

Dear All,

I encountered a problem with a Tempered Water System Design and would like to ask about possible remedies to this problem. I have attached a drawing in Excel for your reference.

This Tempered Water System is used in a Heat Exchanger. There is a vessel to store the water and a pump to pump the water around the system as well as to the air fin cooler to cool the water after it has been used to cool process streams in the heat exchanger. The flow through the air fin cooler and bypass is controlled by a Temperature controller downstream of the valves.

The valves work such that when the flow through the air fin cooler is 100% the bypass is zero and vice versa. The problem however is that if any of the valves (bypass or normal control) is fully opened, the flow rate will be too big and the pump will operate outside the curve and trip.

What are the possible solutions? We have discussed putting a restriction orifice downstream of the pump.

Is it possible also to operate and not allow the valve to fully open? From the curve we can obtain the maximum flow through the pump and from this we can determine the maximum opening for the valves but is this feasible to put into practice?

 Tempered Water System.xlsx   29.19KB   54 downloads

[shan]

RO should be installed downstream of by-pass valve. No downstream of pump.

[yeek]

RO should be installed downstream of by-pass valve. No downstream of pump.

Care to elaborate on this? If the RO is places on the by pass valve but the normal TCV is allowed to open to 100% the pump will still trip because it will cause the flow through the pump to be outside the curve.

[shan]

Under normal operation, tempered water discharged from pump runs through air cooler, TCV, and heat exchanger. The operating point should be the pump design point (BEP) instead of end of curve point.

By the way, I don't think it is necessary to have 2 TCV in your system. You just need control one branch flow and rest of flow will be through the other branch.

[yeek]

Under normal operation, tempered water discharged from pump runs through air cooler, TCV, and heat exchanger. The operating point should be the pump design point (BEP) instead of end of curve point.

By the way, I don't think it is necessary to have 2 TCV in your system. You just need control one branch flow and rest of flow will be through the other branch.

The operating point is already at the pump design point. End of curve happens when the TCV is at 100% opening and causes a flow through the point that is at end of curve.

The 2 valves system is not really the issue here although you could be right.

The point I'm really raising here is whether we can prevent the valve from going to 100% opening during normal operation. If we can't, apart from the RO downstream of the pump what else can be explored.

[shan]

Under normal operation, tempered water discharged from pump runs through air cooler, TCV, and heat exchanger. The operating point should be the pump design point (BEP) instead of end of curve point.

By the way, I don't think it is necessary to have 2 TCV in your system. You just need control one branch flow and rest of flow will be through the other branch.

The operating point is already at the pump design point. End of curve happens when the TCV is at 100% opening and causes a flow through the point that is at end of curve.

The 2 valves system is not really the issue here although you could be right.

The point I'm really raising here is whether we can prevent the valve from going to 100% opening during normal operation. If we can't, apart from the RO downstream of the pump what else can be explored.

[shan]

You may change your current TCV to a smaller one.