RCE was involved with the design of a small refrigeration gas plant. In the span of a single week, RCE through its comprehensive review of vendor data, found two complete “busts” in the vendor designs.
The first was the gas chiller. Initially the shell and tube heat exchanger vendor ignored that there was ethylene glycol (EG) injection occurring just upstream of this exchanger. The initial design proposed by the vendor was approximately 30% undersized because the EG/water phase, while being small in quantity, has a relatively high viscosity which affects the heat transfer coefficient. In the vendor’s next attempt they assumed that the small EG/water fraction coated the tubes, and due to the high viscosity, resulted in the chiller being twice the needed size. In the end, it was pointed out that the gas turbulence would prevent total coating of the tubes with EG/water and the correct size was finally obtained. The use of RCE’s expertise, experience, and our simulation tools, such as HTRI and HYSYS EDR was very valuable.
The second problem was the air-cooled refrigeration condenser. The air cooler vendor’s initial design was 80% undersized because they had calculated the MTD incorrectly. They had performed an end point MTD calculation, whereas, with a refrigeration condenser there is a small de-superheating section followed by the condensing section which is most of the duty and is at a nearly constant temperature for a pure component refrigerant such as propane! This was pointed out to the vendor and they revised their calculations to get an adequately sized condenser. Again, our experience and expertise combined with our tools such as HTRI was the key.
Had RCE not been on the job the plant would have been built with two key exchangers woefully undersized. Another example of RCE adding value to make sure the job gets done right!