The investment in new process control technology for the SAR (Sulphuric Acid Recovery) furnace at our Cassel site in the UK will significantly reduce the variable production cost of the MMA production process.

The SAR furnace at Cassel is used to burn by-product acid from the MMA plants in order to recover the SO2 for acid production. The decomposition reaction desired requires high temperatures. Combusting natural gas with oxygen is used to achieve this. It is the use of these two raw materials that accounts for a significant variable cost in the MMA production process.

An Aspen APC (Advanced Process Control) module has been introduced onto the SAR furnace at Cassel to reduce the consumption of natural gas and oxygen in the process. The APC sits above the site DCS (Distributed Control System) and on top of the normal plant control systems with the capability of analysing many variables and constraints in real time. By modelling the whole system, it can drive the control variables, thus optimising the process whilst maintaining the safety and operational constraints of the plant.

“It is critical that an oxygen excess is retained in the furnace to prevent the formation of a flammable atmosphere in any downstream equipment,” says Andrew Herbert (SAR Lead Development Engineer).

“The new APC had to be configured to ensure that oxygen was maintained at safe levels. It is desirable to reduce the furnace temperature from a cost perspective, but this had to be balanced against the impacts on downstream equipment if sufficient decomposition is not achieved. We therefore also installed a new gas phase ammonia analyser as part of this further plant optimisation to provide a quick and reliable means of detecting insufficient decomposition,” he explains.

The reductions in the amount of oxygen and natural gas consumed by the furnace, while still ensuring sufficient decomposition and oxygen levels are achieved, have been particularly noticeable when changing plant operating rates, as the APC is much more stable and able to make predictions based on its internal models to compensate for planned changes in process conditions. By reducing the use of raw materials in the process, Cassel will make significant savings per annum and the plant’s environmental footprint can be further reduced.