Design an intermediate project storage tank heat exchanger cooling loop.
PRODUCT STORAGE TANK DOUBLE-PIPE HEAT EXCHANGER DESIGN
Process Engineering Associates, LLC (PROCESS) was contracted by the client, a specialty chemical manufacturer, to develop a circulating loop heat exchanger to cool the contents of an intermediate product storage tank. The tank required cooling from 175 oF to 100 oF within an eight (8) hour time period. Throughout the eight hour time period, the tank is continuously filled with hot product effluent from an upstream reactor. A circulating pump draws new product from the tank and routes the stream through a heat exchanger with a return to the tank. The exchanger would be serviced by chilled water from a chiller unit common to the building.
The product contained in the tank is a proprietary solution of low molecular weight esters and ethanol. No physical property data is available in the open literature. As such, there is no relevant physical property data available in any commercial flowsheet simulation program. The first step, therefore, was for PROCESS to regress physical property data obtained from the client to determine the appropriate equation constants for inclusion into the simulator’s physical property calculations.
As the process is dynamic (or transient; a function of time) in nature, a dynamic model was developed in CHEMCAD (commercial flowsheet simulator). The dynamic model included unit operations for the storage tank, circulating pump, and generic heat exchanger. The model was used to determine the duty requirements as a function of time needed to cool the tank contents down to 100 oF within the eight (8) hour time period. A design condition consisting of a specific exchanger duty, hot and cold stream flowrates, and the corresponding hot and cold stream temperatures, was selected for detailed heat exchanger design.
With an exchanger design condition determined as described above, an exchanger type needed to be determined. Aspen Plus’s Exchanger Design and Rating tool was used to evaluate a shell and tube exchanger. The purpose of the evaluation was to determine the overall heat transfer coefficient (U) and exchanger area required. It was found that the shell and tube exchanger would not fit into the space available. A double-pipe exchanger was designed. This exchanger fit within the allotted area and could be fabricated by on-site personnel.
The overall heat transfer coefficient and exchanger area determined via the Aspen model was used in the dynamic CHEMCAD model to determine if the design proposed was sufficient to cool the tank within the specified time limit. It was found to be acceptable. PROCESS submitted the exchanger design details to the client. PROCESS personnel oversaw installation of the process piping and fabrication of the exchanger. The cooling loop is slated for commissioning in the near future.
- Specialty Esters Production
- Dynamic process simulation
- Heat exchanger design