The main steam system applies the bus pipe system, so do the high and low pressure water supply pipes at the inlet and outlet of water supply pump. The outlet of water supply pump is also set with a recirculating pipe and a recirculating bus pipe. The superheated steam generated by two garbage incineration exhaust-heat boilers will converge in the main steam bus pipe and then enter the condensing steam turbine via the main throttle valve to work, thus driving the generator to generate. After that, the steam will be discharged into the condenser to become condensate, which will then enter the deaerator after being pressurized by the condensate pump. After deoxygenization, water 130℃ of will be sent to the exhaust-heat boiler for circular flow.
To meet the requirements of turbo generator set on adjustment, security and lubrication, the turbine generator chamber is also set with a oil system, consisting of oil tank, oil pump, oil cooler, etc.
Chemical Make-up Water System
One line of chemical make-up water from the chemical workshop will flow into the deaerator via the blow down cooler and another will be directly supplemented into the drain tank for recharging the system and boiler.
The sewage from two exhaust-heat boilers will converge to the bus pipe and then flow into a continuous blow down flash tank. The flashed steam will be discharged into the deaerator. The sewage will be discharged into the trench after passing through the regular blow down flash tank.
Drain and Blow-down System
It is set with a drain tank and a drain flash tank. The condensate or drain in devices and pipes of low pressure and chemical make-up water will directly flow into the drain tank. The drain in devices and pipes of higher pressure will flow into the drain tank after the drain flash tank.
The drain and blow-down system is set with two sets of drain pumps, one in operation and one in standby.
Circulating Water System
The circulating water system is set with 2 circulating water pumps. The main devices of circulating water system are condenser and circulating water pumps.
Industrial Water and Cooling Water System
The industrial water system is supplied with industrial water and is set with 2 industrial water supply bus pipes forming a pipe network in the plant.
Layout of Turbine Generator Chamber and Water Supply and Deaerator Chamber
The turbine generator chamber applies a double-layer layout. The steam turbine, main steam valve, generator and exciter are fixed on the operation platform. The auxiliary devices of oil system, e.g. condenser, air cooler, oil cooler, oil pump, etc., are laid at the bottom layer. The thermal deaerator is on the deoxygenization layer.
Technological and Economic Indicators of Operation Conditions
Treatment capacity of the garbage incineration power plant: 700t/d
Number of garbage incinerator: 2 sets
单台炉垃圾处理量： 350 t/d
Treatment capacity of a single incinerator: 350 t/d
Calorific value of garbage under designed operation conditions: 6280kJ/kg
Steam volume generated by a single incinerator under designed operation conditions: 26t/h
Total steam volume: 52t/h
Number of steam turbine generator unit: 2 sets (12MW)
Steam inlet rate of a single steam turbine generator under designed operation conditions: 38.4t/h
In normal production, two boilers and generators will be put into operation and it is considered that the generator and boiler annually operate for 8,000 hours and requires 760 hours of overhaul.
Scope of Electrical Design
The design contents include the electrical designs under the sub-item within the red lines of the plant, including generation and connection system, power for plant, indoor and outdoor lighting, lightning protection and grounding, fire proof, telecommunication, etc.
The design principle to be simple and reliable in respect of the main electrical connection; the layout of electrical devices shall facilitate the operation and maintenance and shall be close and concentrated as much as possible, thus to save investment and operating expenses and lower down cost; the relay protection uses microcomputer protection to correctly and quickly remove faults and comply with the automation requirements of the power plant.
Main Electrical Connection
The preliminary program sets 2 incinerators with the treatment capacity of 350t/d and 2 generator units with the rated power of 6MW.
The power is transmitted to the substations in cities via the overhead lines.
Relay Protection and Automatic Device
The garbage incineration power plant is mainly equipped with the following relay protection and safe automatic device to achieve various protections:
Protection of generator: longitudinal differential protection, over-current protection started by composite voltage, overload protection, over-current protection for single phase grounding of generator, one-point grounding and two-point grounding protection of generator excitation.
Step down transformer protection for operating and emergent purpose: quick-break protection of current, over-current protection, zero sequence current protection, temperature signal, automatic charging equipment of emergency power supply.
Bus protection in segments: over-current protection.
Lighting and Circuit Overhaul
The preliminary program is set with normal lighting, accidental lighting, overhaul lighting and local lighting.
The voltage of lighting network for overhaul and special places can be 12V or 36V.
The overhaul box in the incineration workshop is set at the location specified in regulations and is supplied by the central distribution panel; the auxiliary overhaul box in the incineration is supplied by the power box in each workshop.
The main cable structures in the program are: cable trench, cable shaft, etc. The laying method of cable mainly applies laying along the cable bridge and cable trench, pipe inserting laying and direct burying laying.
The cable structures shall apply fire proof facilities, e.g. fire proof partition, fire proof section, fire proof interlayer, etc., and use such fireproofing materials as coating, trench box, putty, etc., to conduct fire retardant design for cable and meet corresponding regulations.
Fire Fighting System
Fire Fighting System
Reliable fire and explosion proof treatment shall be conducted for inflammable places and electrical devices. Flue gas detectors, temperature detectors and dedicated fire proof alarms shall be installed in places that electrical devices concentrate, e.g. distribution room, control room, etc.
The main comprehensive plant shall be set with a broadcasting system to ensure the issurance of fire alarms, people search broadcasting and various notices.
The scheduling and communication methods for the waste incineration power plant shall be determined through negotiation with local competent departments.
Compositions of Main Control System
The waste incineration power plant applies the automatic control instrument device composed of discrete control system (DCS), local control panel, local instrument, control valve, etc., to control, operate and monitor.
Name and Method of Control System
Wagon balance house
Controlled by independent computer
Garbage unloading gate
Garbage lifting control
Hydraulic discharge system of incinerator
Exhaust-heat boiler system
Flue gas treatment system
Water supply system for steam turbine and deoxygenization
Chemical water treatment system
Comprehensive water system
Fly ash solidification system
Air compressor system
Leachate treatment system
Chemicals feeding, analysis system for boiler water
Other public systems
给排水系统Water Supply and Drainage System
The preliminary program includes the water supply and drainage for the entire plant, including water supply treatment, sewage treatment and water supply and drainage pipe network.
Water source is divided into surface water and running water. The water for waste incineration power plant applies the combination of surface water and running water.
The urban running water can be used as domestic water for the plant and standby water source for chemical desalted water.
Chemical Water System
In view of the security and reliability requirements of the waste incineration power plant, the water supply for boiler shall apply desalted water according to technological requirements.
Schematic Diagram of Chemical Water Treatment Process
Fire Fighting Water Supply System
The fire fighting system for the entire plant is indoor fire hydrant water supply system and outdoor fire hydrant water supply system.
Drainage includes the collection and treatment of domestic sewage, industrial waste water and rainwater.
Drainage applies the system of
The water for submerged chain conveyor, dry ash blender, spiral ash extractor, plant and unloading platform flushing, percolate flushing, vehicle flushing, etc., will be discharged into the drainage pipe network after collection and treatment.
The domestic sewage and industrial waste water will be discharged after meeting the treatment standards.
The rain water will be discharged through the rain water pipeline in the plant.
Waste Water Treatment Process
The domestic sewage and ground washing waste water will be discharged after meeting the treatment standards. The quality of treated water is domestic sewage after class I treatment by the septic tank. Biological treatment technology is applied. The water reaching standards after treatment can be directed discharged.
Aeration adjustment tank
Preaeration adjustment tank applies reinforced concrete structure. It is set with a set of stainless steel mechanical bar screen, two sewage lifting pumps (one in operation and one in standby), one set of full-automatic level controller and one overflow gate. The inside of tank is set with a set of preaeration pipelines, which not only have the effects of preaeration, but also prevent mud deposit in the adjustment tank and smelliness due to the lack of oxygen.
Anaerobic digestion tank
Anaerobic digestion tank applies anti-corrosion structure. The insider of the tank is set with a kind of three-dimensional flexible padding and an air sparger to prevent dead corners and short circuit of water flow. The average designed gas and water ratio of the anaerobic digestion tank is 3:1. The aerator is ceramic post sintering fine bubble aerator.
Contact oxidation tank
Contact oxidation tank applies anti-corrosion structure. The insider of the tank is set with a kind of three-dimensional flexible padding and an air sparger. Meanwhile, multistage partition plates are set in the tank according to actual conditions to prevent dead corners and short circuit of water flow. The contact oxidation tank applies pushing flow uniform aeration and the sewage continues to advance in the biochemical tank, so as to make the biological film on padding completely contact with the organics in sewage and let the organics in sewage to be fully degraded; the designed average gas-water ratio in the biochemical is 12:1. The aerator is ceramic post sintering fine bubble aerator and the use ratio of oxygen is generally five times of that of general perforating aeration. To ensure the removal rate of ammonia nitrogen, the tank is set with 1 backflow water pump.
Secondary sedimentation tank
Secondary sedimentation tank applies anti-corrosion structure and vertical flowing setting. The tank is set with 1 guide cylinder and 1 mud discharge device.
Disinfection tank applies steel structure and disinfectant is solid chlorine tablets.
Sludge tank applies anti-corrosion structure. The sludge in the primary sedimentation tank and secondary sedimentation tank is lifted with steam and sent into the sludge tank. The tank is set with 1 aerator pipe to accelerate the digestion of sludge. The sludge settled in the tank will be transported to the outside by the dung-cart of the Institute of Environmental Health.
烟气净化系统Flue gas Purification System
In normal conditions, the flue gas purification technology is mainly for controlling acid gases (HCl, HF, SOx), NOx, particles, organics, heavy metals, etc. The processing equipment is mainly composed of the following parts: i.e. equipment for removing acid gas removal, capture of particles, removal of NOx and organics and heavy metals.
Acid Gas Removal Technology
Semidry de-acidification generally applies calcium oxide (CaO) or calcium hydroxide (Ca (OH)2) as raw materials for preparing calcium hydroxide (Ca (OH)2) solution as absorbent, which is often placed before the dust removal device, because abundant particles will form in the reaction tower after injecting lime slurry and must be removed by the dust removal device. The volatilization of moisture will reduce the temperature of waste gas and enhance the humidity to let the acid gas react with lime slurry to generate salt, which will fall to the bottom. Direct flow or reverse flow design is applied for flue gas and lime slurry to maintain the contract time for full reaction between the flue gas and lime slurry, so as to obtain high deacidification efficiency.
The lime that does not fully react in the semidry reaction tower will enter the dust removal device with the flue gas. If the dust removal device applies bag type dust removal device, the lime that does not fully react will attach to the filter bag and react with the acid gas passing the filter bag, further enhancing the deacidification efficiency and corresponding enhancing the use ratio of lime slurry.
Characteristics of this method are as follows:
l The deacidification efficiency of semidry reaction tower is higher and its removal rate of HCI can reach the standard (90%). In addition, its removal rate of common organic pollutants and heavy metals is good. If the bag type dust removal device is equipped, the removal rate of heavy metals can completely reach the standards (99%).
l No waste water will be generated. The water consumption is relatively less than that of wet washing tower.
l The process is simple and investment and operating expenses are relatively low.
l The lime slurry preparation system is relatively complicated.
Bag Type Dust Removal Device
The bag type dust removal device can remove particulate pollutants and heavy metals. The bag type dust removal device usually contains multi groups of closed dust collection units, including a number of filter bags supported by cage frame. The flue gas enters the bag type dust removal device from the bottom and flows from down to up. When the flue gas containing dust passes the filter bag, the particulate pollutants will be filtered by the filter cloth and attach to the filter cloth.
Bag type dust removal device can meet the need of removing organics (tetrachlorodibenzo-p-dioxin, etc.) and heavy metals.
Removing Heavy Metals and Tetrachlorodibenzo-p-dioxin
Heavy metals will enter the dust removal device in the solid, liquid and gas state. When the flue gas cools, the part in gas state will transfer into the solid or liquid particles that can be collected. Therefore, the lower the temperature of the flue gas purification system for garbage incineration, the better the purification effects of heavy metals.
The municipal domestic garbage contains a lot of chlorine and organic matters; therefore the flue gas at the outlet of boiler often contains tetrachlorodibenzo-p-dioxin (PCDD, PCDF).
The heavy metals and TCDD removal technology applies active carbon adsorption and bag type dust removal device, which has good removal effects for TCDD and heavy metals. If semi dry purification technology is applies, active carbon will be injected into the pipeline set in front of the dust removal device and dry active carbon will be injected into the pipeline set in front of the dust removal device via the injection fan in a pneumatic form. Heavy metals and TCDD will be absorbed through contracting with the flue gas on the filter bag.
In addition, the control measures for TCDD (PCDD, PCDF) also include the following aspects:
To let garbage fully burn;
To control the stay time and temperature of flue gas in the hearth;
To control the temperature at the entrance to the dust removal device to be below 200℃
When the temperature of the flue gas to enter the dust removal device is 140－160℃, the removal rate of TCDD can be above 99％. The mercury discharge can not be detected.
4、NOx去除 Removing NOx
The NOx removal technologies are selective non-catalytic reduction method (SNCR) and selective catalytic reduction method (SCR).
Selective Catalytic Reduction Method (SCR)
SCR is to restore NOx into N2 with the existence of catalyst. In order to reach the temperature of 400℃ required for the SCR method, the flue gas should be heated before entering the catalytic denitrification device. It is certified through tests that SCR method can control the discharge concentration of NOx below 50mg/Nm3.
Selective Non-catalytic Reduction Method (SNCR)
SNCR is to restore NOx into N2 with reducing agent under high temperature (800－1000℃). SNCR requires no catalyst, but the temperature required for the reduction reaction is higher than that of SCR method, therefore SNCR shall be set to complete in the hearth.
Comparing two methods, SCR method not only requires catalyst, but also requires re-heating after the dust removal device and requires abundant heat, therefore SNCR is more frequently used in project than SCR method.
Currently, it is not suggested set special NOx removal facilities, the specific reasons are as follows:
The investment in SNCR import is higher, so is the use and maintenance fee in later stage.
When used with the burning technology within the boiler, including control O2 and temperature in the boiler etc., the primary concentration of NOx at the exit to boiler will be reduced.
The primary concentration of NOx at the exit to boiler is about 200－600mg/Nm3 and is generally below 300 mg/Nm3, which is approximately close to the discharge index of flue gas. Meanwhile, partial NOx can be removed through active carbon adsorption, lime neutralization reaction and so on.
Currently, the incineration technology can also reach the discharge concentration of 150－400mg/Nm3 without using NOx removal facilities, therefore the program suggests not setting NOx removal facilities, but reserving the interface for SNCR denitrification system in order to save investment and operating and maintenance expenses.
5、烟气净化处理Flue gas Purification Treatment
The pollutants in the flue gas of garbage incineration may be divided into the following four categories:
Acid gas (HCl, HF, Sox, NOx, etc.)
Heavy metals (Hg, Pb, Cr, etc.)
Organic pollutants with hypertoxicity (TCDD, furan, etc.)
To prevent secondary environmental pollution in the garbage incineration process, strict measures must be taken to utilize the flue gas purification system to control the discharge of garbage incineration flue gas. This technology mainly includes the following parts: lime slurry preparation system, spray drying reaction tower system, bag type dust removal system, active carbon system and ash transporting system.
Semidry purification technology selects the process flow of “spray drying reaction tower＋active carbon absorption＋bag type dust removal device”.