In landfill gas utilisation the basic task of the control system is to harmonise three completely independent processes.
- On the one hand, there is the gas production of the landfill which is inconstant. (From a price point of view, hardly worthwhile to store the gas in a gasometer)
- On the other side the independent gas utilisation process, which orientates itself to the requirement of the energy consumer
- Between them, the flare fulfils the important task of burning off safely surplus gas quantities; and should the utilisation plant shut down or become defective, upholds the ecological degassing of the landfill.
A look at the three control loops
Control loop CL 1: gas collection and delivery
The gas collection plant guarantees the safe and ecological degassing of the landfill. Thereby a gas has to be delivered with a CH4 content and other features, that satisfies the requirements of the utiliser.
- The extraction takes place by means of an automatically controlled gas pump, which takes into account fluctuations in gas production within the landfill. The adjustments to the collection system made necessary due to local fluctuations in gas production are carried out manually at the well heads or, either automatically or manually, in a measuring and control station.
Control loop CL 2: gas utilisation
- The individual utilisation units adjust their output to the requirement of the consumer. Consequently the equipment consumes a variable gas quantity with a defined mixture. The enhanced possibilities of control, open up combinations of utilisation units. Cleverly designed combinations of combustion chambers/boilers and engines, contribute to an economical, optimum utilisation.
- Landfill gas and combustion air quantities are adjusted for individual requirements, according to pressure ratios, residual oxygen content of the exhaust gas, etc.
Control loop CL 3: Surplus combustion
- In every landfill gas utilisation system, the flare functions as an important safety element for all risks involved. It - or the combination of flares - are designed, so that during stand-by operation a minimum of energy goes this way, but in an emergency, the whole landfill gas production can be burnt off.
- Varying the combustion capacity of the flare. A combination of flares extends the regulating range considerably: A small flare running with a minimal gas quantity, combined with a stand-by larger flare, guarantees an economically sound utilisation operation.
Control loops of the gas collection and delivery, gas utilization and surplus gas combustion
The interplay of the control loops for gas collection and delivery, gas utilisation and surplus combustion, demands a process control, in order to guarantee at all times:
- the safety and efficiency of the gas collection
- the reliable, economical operation of the utiliser even when there are abnormal occurrences in control loop 1
- the complete and low emission combustion
Hofstetter knows where the problems lie. With the available know-how, the experience and the modular construction of their control systems, an optimal solution can be realised.