Advances in Energy Reduction in Methanol Plant Design

Prior to the Middle East war, 'state of the art' low pressure methanol plants operated with an energy consumption of about 34 million BTU plus 55 kWh per ton of methanol product. Today's plants consume less than 27 million BTU per ton whilst at the same time providing all their own electrical power requirements. This paper describes the sequence of process design improvements that led to these significant savings. Davy McKee maintains an ongoing research program, and recent process improvements which are still under development are outlined. In particular, the paper presents Davy McKee's version of the next generation of synthesis reactor. The paper also examines the economic justification of the energy saving steps. To complement advances in process design, new control strategies are being developed which enable the latest microprocessor-based systems to play their part in energy conservation. Advanced control is discussed in this context using multivariable control of reformer furnaces and optimal control of the methanol synthesis loop as examples. In addition, the paper discusses the roll that dynamic simulation can play in testing control strategies under transient conditions. This technique is becoming more appropriate with the current trend towards larger integrated multiplant complexes and with the falling cost of computing. The conclusion examines the question of whether further improvements can be achieved and, if so, how they will be brought about