BP Amoco was engaged in expanding production capacity for purified terephthalic acid (PTA) at the CAPCO 6 and Zhuhai 1 petrochemical plants in China. PTA is used in the manufacture of polyester resin and polyethylene terephthalate (PET) plastic bottles. It is also widely used in the pharmaceutical, food, textile and packaging industries. The expansion projects were part of efforts to achieve process simplifications and lower capital costs. Project goals were to reduce plot area and the number of equipment pieces by 40%
The process includes up to 530,000 acfm of corrosive exhaust gases that are cooled to the adiabatic saturation temperature. Cooling large flow rate gases is challenging due to potential void spaces in the water spray system. Splitting flows into smaller exhaust trains is a common method to overcome this challenge. However, this adds ductwork and installation cost. For capital cost reductions, the customer wanted to saturate the gas in a single train in a horizontal arrangement to conserve space and to minimize ductwork.
The customer selected a custom engineered Envitech horizonal quencher. The material of construction is Hastelloy C276 to provide corrosion resistance at high inlet temperatures. A proprietary internal water injection and throat design splits the stream inside the vessel to ensure turbulence for mixing gases and water. Gases accelerate through the throat areas in combination with a recirculated water spray system. A small pressure drop cools gases over a wide flow rate operating range and minimizes the number of nozzles. The water spray header is removable to facilitate nozzle replacement and maintenance. The vessel is 13 feet in diameter in a horizontal arrangement. This allows the quencher to be shop fabricated so that inspection and quality assurance are done in a controlled environment. The unit is shipped as one piece.
The Envitech quenchers were installed in 2001 and operate to the design parameters summarized below. The proprietary design contributed to BP Amoco’s goals to reduce footprint area, process equipment pieces, and capital cost.
- Max flow rate: 530,000 acfm
- Inlet temperature: 560oF
- Inlet pressure: 518 In. W.C.
- Guarantee: Cooling to +/- 40oF of the saturation temperature
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