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Ash Gate For Bottom Ash Handling


ASH Gate

AshGates are installed on side of 'V' of Bottom Ash hopper.The Ash Gate has a fabricated housing with its slide type rigid Gate is made of Alloy CI considering heavy dead load on wall. Gate moves on guide rollers and close on taper wedges. The rollers have an eccentric axis which can be adjusted from outside for better locking.The Ash Gate is provided by Man-hole access door, Hand-port Watch glass and Flood light. The Gate is opened by Hydro-pneumatic cylinder in associated with Air-water converter is part of ash gate.

The Ash Gates are available in three sizes 600×600, 600×900 and 900×900.

Bottom Ash Handling System



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.

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, Taiwan2×500 MW
2.Thermax Limited, Chinchwad, BILT-Sabah Forest Industries, Malaysia
3.Parli TPS, Unit 4, MSEB1×210 MW
4.Parli TPS, Unit 5, MSEB6×790 MW
5.Tata Steel, Jamshedpur1×30 MW
6.Kutch Lignite Power Plant, GEB2×70 MW
7.Chandrapur TPS, Unit 4+5, MSEB2×500 MW
8.Vadinar Power Company (ESSAR), Through Thermax (co-Gen plant)


Pneumatic Handling Systems (Ash & Non-Ash)


Technical Details

n all the pneumatic handling systems, the material is conveyed through the pipes with the assistance of air flow, to a closed silo.

The principle of conveying the material through pipes used in "Lean phase vacuum system" & "Lean phase pressure system" is the same. Air flow in the pipe carries the material in a homogeneous mixture and thus a minimum velocity is required to be maintained to ensure that the material does not settle down. The velocity depends on particle size and density of material. As a result the dust to air ratio is generally low and the velocities high.

In the Lean Phase Vacuum System negative pressure is created at the silo end using vacuum pumps. Atmospheric air enters through Air Intake Valves at the material feed end of the conveying pipeline. The material from hoppers is fed to the pipeline using Ash Extraction Valves. Using Cyclone separator and/or Bag Filters mounted over the Silo, material is separated from the conveying air which is sucked by the vacuum pump.

In the Lean Phase Pressure System, pressurized air is injected from the feed point end of the pipeline which carries the material to silo which is kept at atmospheric pressure. The material and air is separated in the same manner using Cyclone separator and/or Bag Filters mounted over the Silo. The material is fed to the conveying pipeline using Ash Extraction Valves. Sometimes a pressure vessel is used below the hopper which acts as a buffer storage vessel to achieve sequential evacuation of hoppers and improving overall efficiency of evacuation. The pressure requirement for this system is low to a level below 1 bar.

In the Dense Phase Pressure System the conveying air virtually pushes the material through the conveying pipe rather than carrying it. Thus in this system the Dust to air ratio is high and velocities are low, however, air pressure required is much higher requiring screw or reciprocating compressors. The air circuit needs to have a big receiver as the air is required in pulses rather than continuous flow. This system has a Pressure vessel below each hopper with a Dome Valve to isolate the vessel from hopper. To start the cycle, first the pressure vessel is filled-up by material from hopper by opening the Dome valve which closes once the vessel is filled. The material collected in the vessel is pushed out of vessel to the conveying pipe by injecting air in the vessel. Once the complete material from the vessel is pushed through the conveying pipe to the silo; the air injection is stopped and the Dome valve is again opened to allow the material to fill the vessel. Air entering silo along with material is vented out through Bag Filters. The system also requires Poppet Valve & Non Return Valve for the injection airline.

All the three systems require Tight Shut-off Valves for the purpose of pipe line selection / diversion.

DEMECH can design and supply complete pneumatic handling system along with all its associated equipment and instrumentations for handling various bulk material.

DEMECH also supplies a pre-assembled set-up called Derropot which is a cost effective solution for handling powdery material at a low rate of 1 to 2 TPH for a short distance.

Salient Features

  • DEMECH can design and supply complete Pneumatic Handling system for Ash and Non-Ash material including manufacturing of all critical components thus ensuring compatibility between various elements of the system.
  • Unique low cost solution in form of Derropot for mini systems.
  • DEMECH has experience of executing systems for handling Ash of more than 850°C. for 500 MW power plant.


Wet Ash Handling Systems



Fly Ash is the major constituent of the ash generated from Pulverized and Fluidized bed Coalfired boilers. The Fly ash gets collected at various points, with most of it in ESP hoppers. One of the methods for handling Fly Ash is Wet system in which the ash is mixed with water to form slurry which is pumped to slurry pit.

Technical Details

The Fly Ash collected in various hoppers is at temperatures more than 100°C. The Hopper outlets are provided with isolation slide plate valves which can be remote operated (pneumatic or motorized) preceded by manual operated slide plate valve. The down flow spout is fitted with Expansion Joint which is followed by Feeder Ejector. A 100 NB water connection from side of Feeder Ejector supplies medium pressure water which mixes with Fly ash to form slurry of concentration upto 35%. This slurry flows out of the Ventury tail piece of the Feeder Ejector by gravity through open sluice trenches or closed pipes and collected at a central point from where centrifugal slurry pumps or Hyjector are used to pump it at the designated slurry pit / main slurry tank for further disposal. The unique DEMECH design of Feeder Ejector ensures that the steam / water vapours generated during mixing of hot Fly ash with water do not rise back to the hopper and clog the hopper outlet.

This is essentially an intermittent operating system with ash removal capacity at a rate of 30 to 60 TPH per Feeder Ejector. Number of Feeder Ejectors operated simultaneously decides the overall ash handling rate and thus the hopper evacuation time and its cycle is computed.

Application Area

Wet system for handling Fly ash for large boilers where the quantity of ash produced is large. The need for such a system becomes important when the Fly ash cannot be utilized further and the disposal pits / ash ponds are located far away from the plant. The water requirement in this system can be reduced by installing water recovery systems to reuse the water back in handling Fly ash.

Salient Features
  • DEMECH can design and supply complete Fly Ash system including manufacturing of all critical components thus ensuring compatibility between various elements of the system.
  • Experience of executing turnkey contracts of many plants where Fly ash has beensuccessfully handled.

Clients Served
1.Koradi TPS, Unit1, MSEB1×120 MW
2.Koradi TPS, Unit6&7, MSEB2×210 MW
3.Parli TPS, Unit 4, MSEB1×210 MW
4.Parli TPS, Unit 5, MSEB1×210 MW
5.Kutch Lignite Power Plant, GEB2×70 MW
6.Chandrapur TPS, Unit 4+5, MSEB2×500 MW


Air Intake Valve


Air Intake Valve

Air intake valve is used in vacuum conveying system. It operates when particular line is selected for conveying operation. Air intake valve has seat and disc in metal, controlled air can be taken in by adjusting the stroke. Protection against ingress of water and foreign particles is provided by adding a hood.

Sizes150 NB (up to 40 TPH) 200 NB (up to 60 TPH)
ShaftSS 410

Ash Extraction Valve/Ash Intake Valve


Ash Extraction Valve/Ash Intake Valve

Ash extraction valve is used in Vacuum conveying system and Lean phase pressure system which is located between hopper and conveying line. Ash extraction valve is metal seated. Seat and disc is made from special alloy steel which gives better life than SS. During the operation the gate is operated by Pneumatic actuator, which ensures that the gate is away from the path of material during operation helping to increase life of the valve & better performance than Conventional Valves.

SizeInlet size 300 NB, Outlet size 150 NB / 200 NB
BodyAlloy CI
DiscSpecial Alloy Steel
GateSpecial Alloy Steel
ActuatorAl. Alloy
StemEN – 8

Tight Shut Off Valve (TSV)


Tight Shut off Valve (TSV)

DEMECH TSV is used as Material Inlet Valve / Material Outlet Valve/ Branch Isolation Valve in Pneumatic Conveying Systems In TSV, Sealing surfaces are machine lapped which does not allow air to exit. The spring loaded discs are held firmly against the path they travel & then shields their sealing surfaces from exposure to any harsh process while the valve is open.

In Common Valves like Ball, Plug or Butterfly, Flow path is restricted when valve is open, Whereas DEMECH TSV offers full port flow through the valve.

Sizes50 NB to 300 NB
BodyCI / CS
Seat & DiscHardened Stainless Steel
ActuatorsManual / Pneumatic Cylinder

ASH Crusher (Clinker Grinder)


ASH Crusher (Clinker Grinder)

DEMECH Ash Crushers (Clinker Grinder) are specially designed for the crushing worst clinker for Bottom Ash of Pulverized fuel coal boiler to particle size of -30 mm.

Ash crusher is driven by set of transmission sprocket, gear box, fluid coupling and motor. Toothed Rollers made of high manganese steel. Housing body is steel fabricated with bearing bracket, bearing housing and bearing covers of Cast Iron. Bearings used are heavy duty self-aligning roller bearings which are well isolated from the ash and water inside the crusher. The side gaps of the rollers are closed by Comb made of manganese Steel and wear plates of Alloy Cast Iron. The spur gears are made of Alloy Steel and hardened.

The bigger size Ash Crusher has rollers in segment form to facilitate operator for easy maintenance.

Pressure Vessel


Pressure Vessel

The DEMECH Pressure vessel comprises one piece body with a top inlet and horizontal outlet at the bottom for conveying material. Mounted on the top inlet is a specially designed DEMECH Dome valve. It has a controlled air supply for conveying the material.

The DEMECH designed Pressure vessel is used where material from number of hoppers is collected and conveyed through a single pipeline. It is also used when it is connected independently with individual piping.

Hyjector (Jet Pump)


Hyjector (JET Pump)

DEMECH Hyjector is designed for the best efficiency and long life. The Nozzle &Ventury throat is designed to suit the application. The slurry can be pumped to a discharge pressure of 30 meters. The main advantage of this equipment is it can operate when the suction is inadequate and chances of air being sucked is high where a normal pump can never operate.

Hyjector design is Robust. Inspection cover is provided on body to remove any larger particle blocking the passage. Nozzle is also available in high alumina ceramic which gives three times life against hardened alloy steel Nozzle tips. The throat piece is made of NiHard material with hardness of 500 to 550 BHN.

Hyjectors are available in various sizes to suit applications of for installation below bottom ash hoppers to emptying drain pits.

Sizes available are - 3"×4", 4"×6", 6"×8" &8"×10"

Feeder Ejector


Feeder Ejector

DEMECH Feeder Ejector can be directly mounted below hopper without any feed elbow. DEMECH feeder ejectors are highly efficient and can create ash slurry of concentration up to 35% to 40% resulting in low water consumption. Assembly is made in four major parts. Discharging angle 450 and 700 are available to suit layout. The water pressure required is about 4 kg/cm². They are available with two capacity ratings and sizes i.e. 30 TPH & 60 TPH and 6"×4"×8" & 8"×4"×8" respectively.

Feeder Ejector is also used for cleaning "Pent House" ash of PF boilers during their shutdown period.

Spherical Dome Valve


Spherical Dome Valve

This valve is used for dense phase pneumatic handling system, primarily above the Pressure vessel. In open Position, Spherical Dome is completely out of the conveying path, hence there is no obstruction for material flow. Spherical dome is protected from direct contact with the conveying material.

Sizes100 NB to 300 NB
Body and DomeMS / CI / SS 316 / SS304
SeatNeoprene / EPDM / Silicon / PTFE
Protection CoatingsChrome / PU / Epoxy Resin / PTFE
ActuatorsManual / Rec. Cylinder / Vane Type / Rack & Pinion

*Options available depending upon Application.

To,Deccan Mechanical & Chemical Industries Private Limited

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