Waste incineration power generation
Power generationthrough waste incineration is mainlycomposed of measurement in plant, waste pretreatment, waste incinerator,monitoring of steam turbine, plant power and electrical system, exhaust gastreatment and production management. Three kinds of incinerators are mainlyadopted in current waste incineration: grate type waste incinerator, fluidizedbed waste incinerator and rotary kiln waste incinerator, in which the first twoincinerators are mainly used for municipal solid wastes, while the thirdincinerator has no steam turbine generator and is mainly used for medicalwastes and toxic industrial waste.
II. Solution of gratetype waste incinerator
Typical grate type waste incinerator ismainly composed of waste conveying and ash system, wind and smoke system andthe steam and water system.
2.1Control plan of grate type waste incinerator
It is the special characteristics offuels used that lead to the unique technical process and system structure ofgrate type waste incinerator and this is why incinerators and boilers poweredby different fuels have different control plans, which can be manifested incontrolling systems such as hearth temperature control, load control andcontrol of back spraying flow of leachate.
Hearth temperature control
The hearth temperature control of gratetype waste incinerator is realized by SUPCON in two stages. In Stage 1, the setis started and the hearth temperature will reach “850℃/2S” by start-upburner (or auxiliary burner if the start-up burner fails) since there are nowastes inside. The waste feeding door will be automatically opened and wasteswill be fed until the hearth temperature reaches the standard; the wasteburning load increases along with increasing feeding capacity and the start-upburner controlled by burner management module will have fewer loads and finallybe shut down in turns and the temperature of incinerator is maintained by heatfrom burned wastes. In Stage 2, the hearth temperature shall be kept at “850℃/2S” and the external load shall besatisfied by constantly correcting set value of hearth temperature “T2S”according to load changes of boiler (the change of main stream flow). In casethe heat from burned wastes fails to reach “T2S”, the burner management modulewill determine if it is needed to start auxiliary burner and implement loaddistribution for it.
Based onreal-time calculation of heat value from burned wastes and calculation of airand stream volume, the control plan of central control room can get the averagefeeding speed and waiting speed of waste feeder and moving speed of grate andcan control the movement of waste feeder and grate by sending the calculatedresults to hydraulic system, thus combining analog quantity and switching valueand solving the problem of unstable combustion due to the changes of heat valuefrom burned wastes. As the pioneer in realizing automatic control of feedingsystem and grate drive system by using DCS in China, SUPCON has grasped thecore technology in automatic control of such wasteincinerators.
Control of back spraying flow ofleachate
The leachate flowmust be properly adjusted according to combustion conditions of incineratorsince the hearth temperature can be greatly affected by backflow quantity ofleachate, which it is processed by spraying it into hearth for burning in mostof waste incineration plants. SUPCON can control backflow quantity of leachatein a reliable way by developing leachate control module based on foreignexperience and actual situation of China.
Control offlow and concentration of lime mortar
For the purpose of complying withnational environmental protection requirements for gas emission, SUPCON succeeds in controlling flow andconcentration of lime mortar through calculations based on smoke compositionsand inlet temperature of bag-type dust collector.
III. Control plan of circulating fluidizedbed waste incinerator
Mainly composed of waste conveying and ashsystem, wind and smoke system and the steam and water system, the typical circulating fluidizedbed waste incinerator is newly provided with waste pretreatment system and coldslag system; otherwise, it will have the similar technical processes with gratetype waste incinerator.
3.1Control plan of circulating fluidized bed wasteincinerator
Control ofhearth temperature
There is no control requirement of 850℃/2Ssince no wastes will be fed during startup stage of boiler; after the wastesare fed in incinerator, the heat mainly comes from burned wastes and the coalscan be gradually reduced and used as auxiliary materials to adjust hearthtemperature, which represents the characteristics and design concept thisincinerator. By calculating gas temperature at hearth outlet and its changerates, SUPCON cancontrol hearth temperature with coal management module.
Bycombining PID module and waste-coal proportional allocation module, SUPCON cancontrol boiler load through simultaneous adjustment of wastes and coal.
Control of bed temperature ofcirculating fluidized bed waste incinerator
Restricted by inferior coal and low heatvalue from burned wastes, the circulating fluidized bed waste incinerator haslow bed temperature, which can be controlled by adjusting the proportion ofprimary and secondary air and establishing expert rule base.
Control of sulfur dioxide emission fromcirculating fluidized bed waste incinerator
The sulfur dioxide emission fromcirculating fluidized bed waste incinerator can be controlled through feedingcontrol system of limestone; the measured value and set value of sulfur dioxideare sent to primary controller together for PID calculation and the result isused as the set value of PID control loop of lime stone.