Bottom Ash Handling System

Overview

DEMECH provides variety of systems to handle Bottom Ash or Bed Ash generated by the solid fuel fired boilers. The system has to be selected based on many factors like type of boiler, size of boiler, amount of Bottom ash generated, method of final handling etc. Factors like availability of other resources like water, land etc. also need to be considered while selecting the system. DEMECH can supply following systems


  • 1. Intermittent operating system using water impounded Bottom Ash Hopper with Hyjector and slurry disposal to pond or     to Hydrobin.
  • 2. Continuous operating Submerged Scraper conveyor to removal of Bottom ash.
  • 3. Continuous removal of Dry Bottom ash using water cooled screw conveyor.
Technical Details

Bottom Ash System using Water impounded Bottom ash Hopper

This system can be used for any type of boiler, but as it needs more clear head room below the furnace, thus this system is generally used for pulverized fuel fired boilers. The system has a water filled hopper inside lined with castable refractory which collects the Bottom ash falling from the furnace. The hopper has to be custom designed to match the furnace outlet which is air locked using water seal trough at the top of the hopper. One or more Ash Gates mounted on the lower taper portion of the hopper are used for extracting the ash with water through double or single roller Ash Crusher to the Hyjector (Jet Pump). The Hyjector can pump the crushed ash to a Hydrobin(de-watering bins) or slurry sump from where the slurry pumps are used to dispose the Bottom ash slurry to designated ash pond. The rate of ash removal process is much higher than the collection rate hence this system is operated intermittently by allowing to collect the Bottom ash in the hopper and removal once in eight or four hours.

Bottom Ash System using Submerged Scraper Conveyor

This is a continuous ash removal system with some provision of collection of ash for few hours to undertake minor maintenance / repairs. The system utilizes a Submerged Scraper Conveyor (SSC) to remove the Bottom ash falling from the furnace in the water filled in the conveyor trough portion. The SSC can be fixed installed or mounted on trolley wheel so that it can be rolled out for maintenance. The discharge from the SSC is either allowed to fall in sluice trenches for transportation using water jets for ultimately disposing as slurry or stored in bin using belt conveyors for further disposal by trucks. An associated water circulation system is required to cool the overflow water from the SSC trough. This system needs lesser head room and hence can be used in almost all types of boilers.

DEMECH has entered into technical collaboration with Hitachi Power Europe, GmbH, Duisburg, Germany for the Bottom Ash Handling System using SSC. This tie-up covers system for large boilers.

Bottom Ash System using Water Cooled Screw Conveyor

This continuous operating system utilizes Water Cooled Screw Conveyors to cool and remove the Bottom ash. This system is ideally useful for handling Bed ash from CFBC boilers due to their discharge from specific spouts rather than from a bigger opening. Depending on the number and location of downcommer spouts from CFBC boilers a bank of Water Cooled Screw Conveyors are employed which convey the ash to a Chain Elevator to be transferred to a bin for further disposal by trucks. Slide plate valves with expansion joints in the inlet spouts to Screw conveyors are also provided. The complete system has to be in high grade Stainless Steel material as it handles ash at nearly 800°C. An associated cooling water system is also required. This system requires a low head room below the furnace and virtually no water consumption.

Application Area
  • Bottom ash handling system is required for any solid fuel fired system, however, DEMECH supplies these systems to mainly coal / lignite fired boilers. The problem with first two systems using water as active ingredient has problem handling fuel which is lighter than water since the unburnt fuel tends to float on the water making it difficult to remove.
  • The dry system using Screw conveyor is suitable for the CFBC boilers. An added advantage is that the Bed ash handled in dry form which can be directly used for preparing bed for the CFBC boiler. This system also does not require any auxiliary system to handle drained water from the wet ash collected in the bin as the ash remains dry.
Salient Features
  • DEMECH can design and supply complete Bottom Ash system including manufacturing of all critical components thus ensuring compatibility between various elements of the system.
  • Long term collaboration agreement with Hitachi Power Europe GmbH ensures knowledge of best design engineering and new developments taking place to give better systems.
  • DEMECH has experience of manufacturing and successfully commissioning Water Cooled Screw conveyors handling material of temperature more than 850°C.
Clients Served
1. Taichung Power Plant, Taiwan 2×500 MW
2. Thermax Limited, Chinchwad, BILT-Sabah Forest Industries, Malaysia
3. Parli TPS, Unit 4, MSEB 1×210 MW
4. Parli TPS, Unit 5, MSEB 6×790 MW
5. Tata Steel, Jamshedpur 1×30 MW
6. Kutch Lignite Power Plant, GEB 2×70 MW
7. Chandrapur TPS, Unit 4+5, MSEB 2×500 MW
8. Vadinar Power Company (ESSAR), Through Thermax (co-Gen plant)