Biomass Gasification

Transcription

1 Biomass Gasification Efficient use of Energy Turning waste to energy, liabilities to assets and visions into reality.

2 Table of Contents THE HTI ADVANTAGE FEED SYSTEMS GASIFIERS LOW NOx OXIDIZER BOILER AND EVAPORATIVE COOLER AIR POLLUTION CONTROL CONTROLS CERAMIC HEAT EXCHANGERS TURBINE GENERATOR SETS GENERAL DATA Turning waste to energy, liabilities to assets and visions into reality.

3 THE HTI ADVANTAGE HTI manufactures custom designed process equipment, specializing in biomass gasification/electric power generation systems that convert solid and semi solid biomass, such as animal manures, agricultural waste, solid waste from landfills, waste water treatment sludges, sewer sludges and hazardous waste material into a combustible syngas that can be used to power generators, dryers, heaters and cooling equipment. All gas and electricity that is produced is carbon neutral and considered environmentally Green. The HTI system is designed to handle mixtures of solid wastes with minimal or no segregation. FEED SYSTEMS Three standard feeders are available. The first is a patented, reducing screw shredder feeder (I) designed to process loose paper, plastics, pallets, cardboard, railroad ties, municipal trash and industrial wastes. The feeder is complete with an anti-jamming device and safety shutoff valve. It will shred and charge noncombustible materials, such as stone, cans and bottles, along with combustible materials such as garbage and trash, thus reducing waste segregation to a minimum. This machine feeds the gasifier continuously and the reducing screw maintains a plug in the feeder tube which minimizes the possibility of feeder fires or flashbacks. When compared to ram feeders, the continuous charging reduces temperature spikes. Second, with uniform waste, such as biomass, sawdust, wood chips, poultry litter, etc., the company would supply a mixing feeder without the shredder feature. This device will feed continuously and maintain a feed tube plug as described above. A third proprietary feeder is designed to charge packaged waste in cartons or fiber drums. This HTI proven ram style feeder will take packaged goods from an indexing conveyor into the side of the feeder. Also, loose trash or municipal waste can be introduced through a top-fed charge hopper. HTI engineers will design the material handling system and select the most efficient feeder depending on the waste characteristics. GASIFIERS Several styles of HTI continuous gasifiers are available: a) Medium temperature, parallel flow or counterflow, oxidizing kiln. This is generally used in small industrial or municipal waste plants. b) High temperature, parallel flow oxidizing kiln. This slagging kiln is held near the melting point of the noncombustible solids. It is used when destroying hazardous or highly toxic wastes. c) Low temperature, starved air, counterflow rotary kiln (VIII). This rapid response gasifier is used for handling biomass wastes that lend themselves to volatilization of hydrocarbons and the evaporation of water at moderate temperatures. The syngas is burned in a secondary oxidizing chamber. HTI s rotary kiln (patent pending) is a unique dual shell, refractory lined machine. The air that is forced between the two shells cools the seals and is injected at controlled amounts into the gasifier tuyeres. The gasifier is zoned. Zone one preheats the waste and drives off the moisture and volatiles. Primary or partial combustion takes place in zone two where air flow is controlled through the rotating ceramic tuyeres. Zone three is where the ash is cooled. Rotary gasifiers are superior to grate style incinerators in that they tumble the solid wastes against the high temperature refractory surfaces. The unique HTI concept of zoned drying, partial combustion and cooling while moving the waste slowly through the machine, promotes controlled volatilization without high fly ash carryover. The gasifiers are supplied with an auxiliary fuel burner to ignite the wastes and level temperature spiking by Turning waste to energy, liabilities to assets and visions into reality. 1

4 introducing additional air and/or fuel in the event slugs of water or noncombustible are charged into the unit. d) Low temperature, starved air cell gasifier (II). This patented and proven-inservice cell transports the waste through an airlocked bottom fed system supplied with counter flow augers that prevent bridging and maintain a seal between the gasification chamber and the feed hopper. The waste is forced up through a center cone and a percentage of the stoichiometric air is introduced into the waste pile through tuyeres. This air (ambient or heated) is carefully controlled to maintain a low gasification temperature above the fuel pile between 400 F and 1,000 F. Ash is removed through a series of guillotine gates at the base of the cell and conveyed away from the machine by screw conveyors that, similar to the feed system, maintain an airlock. The continuous feed, coupled with slow burning and continuous ash removal, provides a uniform flue gas discharge at a constant temperature with very low particulate carryover. Machines gasifying sludge and wood wastes are in service today that are using no auxiliary fuel, are not connected to an air pollution control system, and are operating well below stringent particulate air emission codes. When flammable waste liquids are available, HTI auxiliary burners will fire the liquids in lieu of natural gas or fuel oil. When sludges have to be destroyed, a separate sludge feed system is furnished that will charge the gasifier with this waste fuel at a controlled rate, in conjunction with one of the solid waste feeders described above. LOW NOx OXIDIZER This refractory-lined chamber (III) will retain the flue gas at a predetermined temperature. When hazardous, municipal and industrial wastes are being destroyed, the retention times and temperatures are mandated by code. HTI supplies a secondary chamber as part of all solid waste systems to insure complete destruction of the hydrocarbons. The auxiliary burner fires only as needed to control exit temperature and/or to level temperature spikes. A patent pending feature is the staged introduction of heated combustion and tempering air through ceramic nozzles along the chamber length. This staging results in considerable reduction of NOx formation. The chamber can be arranged in either the vertical or horizontal position. If there is a system upset, such as an utility failure, the emergency relief stack will open automatically. This essential safety device, which is located above the oxidizer exit, is set at a sufficient height to keep a negative natural draft at the exit. As soon as the upset condition has been corrected, the emergency relief stack lid will close and normal operations will resume. BOILER AND EVAPORATIVE COOLER HTI recommends a water tube boiler (V) complete with soot blowers. The water tube boiler, which is a highly efficient, reliable machine, lends itself to easy routine maintenance. In some applications, fire tube boilers are used, usually when destroying low-ash waste or when low pressure process steam is required. In either case, the boiler and economizer are sized to insure that the flue gas exit temperature stays above the dew point throughout the turndown range. Depending on waste chemistry, HTI incorporates, as part of the heat recovery system, an evaporative cooler, economizer or air-to-air heat exchanger. In the latter two cases, the heat is used elsewhere in the system and increases plant efficiency. In all three instances, the flue gas temperature is monitored and controlled as it enters the air pollution control system. Turning waste to energy, liabilities to assets and visions into reality. 2

5 AIR POLLUTION CONTROL When required by code, an air pollution control (APC) train is included as an integral part of the HTI system. HTI has supplied lime injectors in line with a fabric filter baghouse (IX). The former neutralizes the acids and the latter removes particulate below code levels. The baghouse is an accepted air cleaning device when burning municipal or industrial waste. A wet packed acid scrubber, electrostatic precipitator or ionizing wet scrubber is available if the waste is hazardous or if its particular chemistry requires special scrubbing techniques. CONTROLS HTI installations are furnished with a computerized control system. The controls permit adjusting the solid waste feed rate and all system temperatures. Every critical control point is backed with an interlock that will alarm and/or adjust air and fuel flow in the event of malfunction. A pressure controller is integrated into the system that will maintain a preset negative draft at the gasifier exit by damper or variable speed control at the induced draft fan (IV). The degree of automation in the controls allows the operator to spend his time overseeing waste charging and ash removal. CERAMIC HEAT EXCHANGERS Two patented, all-ceramic/air-to-air, shell and tube heat exchangers are available. This self-cleaning feature protects the boiler and reduces downtime for maintenance. The second heat exchanger is a high differential pressure machine (VII) that will indirectly heat air to temperatures and pressures up to 2000 F and 200 psig, respectively. This air is then sent to an air turbine to produce power. The high pressure heat exchanger is used in lieu of the boiler in power plants and is used with a boiler in cogeneration facilities. TURBINE GENERATOR SETS An air turbine generator set will be supplied with the high pressure heat exchanger described above. This system is more efficient than the conventional steam turbine plant and also benefits from lower capital cost, lower maintenance and can be operated with fewer personnel. The clean, hot air being discharged from the air turbine is used as preheated combustion air in the oxidizer or can be used in the process. For example, it can be used in a wood or sludge dryer. GENERAL The overleaf shows a biomass plant that will gasify 100 tons per day of chicken litter, produce 16,700 lbs/hr of process steam, and generate two megawatts of power. Similar systems are available for processing municipal solid waste, sludge, wood chips, sawdust, industrial trash, tires, etc. The first is a low differential pressure, high temperature machine (VI) that can be installed between the oxidizer and the boiler. This device is used when the process gas will be exiting the oxidizer at temperatures above 1700 F when the gas contains molten particulate such as silicon dioxide. The exchanger will reduce the temperature to 1550 F and send the clean/heated air back to the gasifier or oxidizer. If the particulate starts to foul the exchanger tubes, thereby increasing the boiler inlet temperature, the operator can reduce the air flow through the tubes and melt the slag. Turning waste to energy, liabilities to assets and visions into reality. 3

6 Turning waste to energy, liabilities to assets and visions into reality. 4