Energy and Capital Savings in DME Process Design and Integration

In recent years, dimethyl ether (DME) is widely used as a feed for the synthesis of chemicals including acetic acid and its esters and as a hydrogen source for fuel cells. The major process for the production of DME on an industrial scale comprises dehydration of methanol using an acidic dehydration catalyst in a fixed bed reactor followed by rectification of the product stream to recover high purity DME. An important motivation for studying integrated distillation processes is to reduce the energy consumption. Basically, distillation (batch or continuous) is an energy intensive process and consumes large amount of thermal energy (via steam), so even small improvements which become widely used, can save huge amounts of energy. The main focus in this work is to apply the heat-integrated and reactive distillation designs on DME process using the steady state approach. Here, the energy and capital cost saving of each design and the environmental impacts have been considered and compared with that by the conventional process.

An observation result using heat-integrated design of the process shows that a significant operating cost savings of 50% compared to the conventional process. The reactive DME distillation column design results show that the highest savings in the capital cost of 69 % and operating cost of 84 % can be achieved compared with the conventional base case. Fundamentally, the saving in capital and operating costs will be directly saving the total annual cost and this saving shows the benefit of using the process integration rather than conventional process. Beside the cost saving, the flue gas emissions have been reduced significantly. The total emissions have been reduced by 51% and 86% using the heat-integrated design and the reactive distillation column design respectively.