We are experienced solving complex and difficult control problems and calculating compensated process indications. If conventional techniques, cascade, feedforward, tuning using Ziegler and Nichols open loop response curves etc. prove unsuccessful in obtaining the required control specification, modelling the process and control system can provide the insight to the system responses and interactions. Using this data combined with G&L's experience inevitably finds a solution to obtain an acceptable, repeatable control system.

These pages show a very abbreviated model to demonstrate our ability in this discipline. The model shown was developed to control the NOx emissions from a reformer flue. Environmental legislation required that emissions did not exceed 19 mg/m3 STP corrected to 12% CO2 dry. This corresponded to 20ppm NOx in the flue gas. The process required the reformer load to rapidly vary by 60% every 24 hours. At 40% load excess air was 40% and at 100% load excess air was 60%. Excess air was the main contributory factor in producing thermal NOx, but during load changes the air lead the fuel, which resulted in a non linear system response. The client, to ensure discharges were maintained within the legal requirements was maintaining discharges at 5ppm under steady state conditions, which increased to 18-19ppm during load changes. The NOx was controlled by injecting ammonia into the flue. The ammonia costs were a significant operating cost.

NO analysers measured the Nitrogen entering the flue and the Nitrogen discharged to atmosphere. An O2 analyser measured the oxygen content of the gas.

The slow response time of the wet gas analysers resulted in an unstable control system that could not maintain the NOx discharges within the legal requirements, rendering the client liable to prosecution for pollution offences.

For examples of the model click on one of the pages below