Use of excess heat from ethylene recycling in a low-density polyethylene production plant

• Autor(a) principal: Matos, Rodolfo D. C.
• Data de Publicação: 2018
• Outros Autores: João, Isabel, Silva, João
• Tipo de documento: Artigo
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10400.21/8710
• topic: Excess heat; Energy efficiency; Economic evaluation

The recovery of the wasted heat is an effective way of improving the energy efficiency of industry sites and can contribute to the reduction of the operating costs and the CO2 emissions. In the production of low density polyethylene, the polymerisation reaction is carried out with a large excess of ethylene at very high pressure. The excess ethylene is separated at an intermediate pressure (around 280 bar and 310 °C) and then it is recycled. In this recycle, the stream is cooled in several steps to temperatures close to 35 °C before being recompressed. In some units, the first cooling is carried out with air coolers up to temperatures around 130 °C. In a unit with a recycle of 33 t/h, this cooling corresponds to releasing to the atmosphere about 4.6 MW of thermal power. We present a study of different alternatives for the use of this excess heat. We studied the implementation of a refrigeration cycle by absorption with LiBr/H2O, the production of steam and the electricity generation by Rankine and Kalina cycles. The Aspen HYSYS process simulator was used to study the different alternatives. The capital cost was estimated for each of the evaluated options as well as the benefits expected to be obtained. In the study conditions, the absorption refrigeration cycle is the best solution presenting a return period of 3 years.