Coal-fired power plant owners and operators are always looking for ways to reduce costs and remain competitive. For factories facing high compliance costs associated with new regulations, closures and gas conversions have become commonplace. The crusher-conveyor technology for bottom ash conversion can result in significant savings in capital and operating costs, and can keep existing coal-fired units operational in the face of such challenges.
The federal government’s new regulations and pending regulations for the storage and disposal of coal-fired residues (CCR) are driving new technologies for converting many coal-fired power plants into bottom ash transportation. Traditionally, plants in the United States spray bottom ash onto surface deposits where solids precipitate. The US Environmental Protection Agency (EPA) regulations are designed to mitigate the environmental hazards connected with long-term loading of ash and effluent discharges. The EPA’s Law on the Disposal of Coal Burning Residues in Electric Conveniences has forced many factories to renovate their ash handling systems to meet the least standards set by such stagnant water rules.
The Effluent Limitations Guidelines (ELG) can ambition alternative trend of adaptations while the current regulations for lowest ash transport water are suspended, while the EPA is considering revisions to the flow and flue gas desulfurization arrangement wastewater. If maintained as intended, ELG will establish zero emission requirements for lowest ash carriage water, which will effectively exclude the use of the lowest tank for the lowest ash.
In the publication of these rules, industrial original equipment manufacturers (OEMs) have developed a variety of technologies to accommodate landfills in the lowest ash instead of surface water storage. Unique method is a power-driven grind system placed directly beneath the boiler where the bottom ash falls into a tank hopper containing water with a chain conveyor at the bottom. In this system, water acts to reduce and break the hot ash, while the conveyor belt drags the ash up to drain the water. The resulting wet ash can then be shipped to a landfill. This technology has been around for many years and has been favored by new factories in recent times.
In ELG, the EPA recognizes two technologies (mechanical resistance systems or remote mechanical resistance systems) as economically feasible BAT. The EPA notes that due to the potential space limitations of some boilers, it is necessary to include remote system options and to recognize that the mechanical strength system of the boiler chassis is large and invasive and can be later installed on existing installations. Indeed, because of the steel structure, coal mills, ducts, steam pipes and other equipment in the area, most factories cannot install large conveyors without large-scale construction. In addition, the lower ash hopper is often located in the tread pit, making the transformation of the traditional traction system almost impossible. Even in some cases, these conveyors can be installed later and construction costs remain high due to basic demolition and replacement of large ash hoppers.
The new regulations specifically developed remote mechanical resistance systems for the market. Its value is that the hopper and hydraulic discharge system at the bottom of the furnace remains essentially intact, while the trailing conveyor is located away from the backyard boiler area. ‘plant. Instead of pouring the bottom ash into the basin, the stream is transferred to a remote conveyor where the solids are poured and dewatered in the same manner as the conveyor below the boiler. However, the essential difference from remote systems is that, in contrast to quenching water, all system water is defined as transport water, and according to the proposed ELG, transport water is required to meet zero emissions requirements. This means that all water in the system must be recycled, which can significantly increase capital as well as operating and maintenance costs.
Clearly, the identified BAT options had two drawbacks, and new technology emerged after the ELG was released, in which the boiler chain conveyor would be installed under the existing ashtray. This technology can solve the problem of insufficient space and low installation costs, which are related to the traditional mechanical drag system of the boiler, while avoiding the requirements of transport water and zero emissions. In recent years it has been recognized and has been successful in three operational units, the other two being under structure.
An essential feature of the new conveyor system is that the clinker mill is used to grind the ashes before they are introduced into the conveyor. These are the same type of crusher as used in the door system and are used to reduce the size before transporting the pipe. In many cases, after the installation of a new conveyor system, the old mill can be held in place with the hopper and the door.
The crusher is a key function of the fixed hopper. The conveyor must be small because there are usually only a few feet of clearance under the hopper. The chain conveyors of the conventional boiler are large and can remove the largest clinker without crushing. However, for the new mill-conveyor system, the size of the conveyor housing is only required to meet the required volumetric clearance without going through a single large clinker. The typical profile of the crusher-conveyor housing is about two feet high and two to three feet wide.
Conventional tow chains and mill-conveyor tow chains have parallel chains traversed by steel scrapers to drive the ashes along the path of travel. Once the ash has reached the top of the ramp, it flows into the chute. The chain and chain assembly rotate 180 degrees around the main gear, then descends the boom and travels to the end of the conveyor.
A conventional conveyor is called a higher load conveyor because the ash stroke of the chain is greater than the return stroke, while the bottom of the submerged hopper separates the two. The reflux operation is called a dehydrated operation because it is not immersed in water. This arrangement should be such that the chain is above the water level in the hopper at both the head and the end. Considering that the water level is generally about 15 feet above the ground and allows some distance traveled above the surface of the water on the inclined surface for dewatering, it is clear that a such a system is difficult to adapt in an overcrowded factory.
Once the crusher has been added to the crusher-conveyor system, the head and tail of the conveyor are kept below the water level. This provides the flexibility to transfer on subsequent conveyors underwater and to arrange a series of conveyors to maintain a lower altitude until the game is reached to get it over the water level of the boat and the hopper usually to the end. The conveyor is located in the boiler room and is disposed of outside trash.
The crusher machine makes this possible because the chain conveyor can be configured to be loaded from the bottom and the return stroke is greater than the feed stroke in the water bath. Once the comminuted ash disappears, they can pass over the return raceway, the return raceway is only supported under the chain, and the steps are suspended, meaning that there is no ground separating the checked and returning raceways. This creates a fully enclosed conveyor with the added benefit of eliminating backflow and residual ash adhering to the web during reflow, which is a traditional underground boiler conveyor and remote conveyor difficult.
Another interesting feature of the crusher-conveyor system is that redundancy can often be integrated into the conveyor configuration. For hoppers with double grinders on each leg, a grinder conveyor can be installed to pick up all grinders on one side of the leg and a 100% separate group can be installed under the other set. This is not possible in a conventional bottom boiler design because there is only one conveyor at the bottom of the deep bottomed hopper, which requires a downtime to repair the breakage of the chain or to remove obstructions in the ash collection area.
Even with a single crush-conveyor unit, most maintenance work does not require interruption of the equipment, as the conveyor can be isolated from the ash hopper by closing the hopper door above the grinder. and closing the auxiliary isolation door located under the crusher. Thus, since the ashes are collected in a pre-existing ash hopper, the boiler can continue to operate until the end of maintenance.
Plant operators who chose the coal conveying technology to complete their residual ash conversion project opted to reduce capital expenditures (equipment and installation) due to exceptional design features. Compared to competing technologies, this technology saves a lot of operating and maintenance costs. This technology can remotely control the dehydration equipment through the door and can also pneumatically transport the ashes to the storage bin. Pumps and fans used in these systems are energy efficient compared to chain conveyors