OCR Text |
Show Group, have increased its production from 500 to 1000 doors per week by converting from the slow process of hot air dryers, to a catalytic combustion system. A much superior finish has also been found. Although these commercial examples clearly show benefits of catalytic combustion, there is an ongoing problem with these heaters in terms of so-called, methane slip, which is due to incomplete combustion at these low temperatures: typically less than 500°C. For many units the methane slip amounts to between 3 and 1 0 % or even higher, which poses a potential problem with C O and N Ox emissions. B G Technology, working with a number of partners and supported by U K Government funding (ETSU), has developed a new catalyst formulation which has produced a methane slip in the region of 1.3% for a commercial prototype. Advanced Controls:- Potentially further energy savings and emission improvements can be obtained with the new-development new burner, furnace and boiler control systems. One such development is the use of bilinear control systems. Bilinear controllers are retrofit devices which are cascaded with a linear PID controller (Proportional / Integral / Derivative) in an existing high temperature control system: Figure 9. The standard PID controller assumes that the process is linear - for example, when its steady state input is doubled, its steady state output is also doubled - whereas in practice most real processes are nonlinear. The bilinear controller uses the measured temperature to gain information about the operating conditions and then modifies the control action of the PID to take into account non-linearity of the process and minimise deviations from the set point. In other words, it provides automatic adjustment of the PID tuning parameters as the point of operation changes. The result of including this bilinear unit in the control system on a multi-burner, continuous furnace with regenerative burners, has been shown to given an energy savings of around 5%. BG Technology pioneered much of the early development and is working with a number of partners to extend the technology on a wider range of high temperature furnace applications. The development is supported by the UK's Energy Efficiency Best Practice Programme. Further work is currently underway at Avesta Steel, Sheffield, to the develop an auto-tuning facility of the bilinear term within the bilinear / PID control system. Longer term, development from bilinear controllers and other modern control systems will offer considerable energy savings, especially when linked to real-time simulations of the heating plant performance (see below). |