Grate: Difference between revisions

Line 59:

*Mixing of flue gases

===Auxiliary Burners===

Auxiliary burners are used at start up to heat the furnace to a required temperature before the waste is introduced. If the temperature falls below the desired value during operation, the burners are switched on automatically. The burners are utilised for shutdown to maintain the furnace temperature and ensure there is no unburnt waste left in the furnace.

==Different Grate Types==

The incineration grate can be categorised generally by feeder principles: continuous (roller and chain grates) and discontinuous (push grates). Grate systems can also be characterised by the way waste is conveyed through zones in the combustion chamber. Each must fulfil requirements regarding primary air feeding, conveying velocity, and mixing of waste. Other features include additional controls or a more robust construction to withstand the severe conditions in the combustion chamber.

===Rocking grate===

The rocking grate sections are placed across the width of the furnace. Alternative rows are mechanically pivoted or rocked to produce an upward and forward motion which advances and agitates the waste.

===Reciprocating grate===

The reciprocating grate sections span the width of the furnace and are stacked above each other. Alternative grate sections slide back and forth, while the adjustment sections remain fixed. Waste tumbles off the fixed portion and is agitated and mixed as it moves along the grate. Different variations of this type of grate exist, such as some with alternating fixed and moving sections, while others have combinations of several moving sections to each fixed section. In the latter case, the sections can either move together or at different times in the cycle.

There are two main variations for reciprocating grates:

====Reverse reciprocating grate====

The grate bars move back and forth in the reverse direction to the flow of waste. The grate is flopped from the feed end to the ash discharge end and is comprised of fixed and moving grate steps.

====Push forward grate====

The grate bars form a series of many steps that move horizontally and push the waste in the direction of the ash discharge.

===Travelling grate===

The travelling grate type consists of a continuous metal belt conveyor interlocking linkage that move along the length of the furnace. The reduced potential to agitate the waste (mixing only occurs when waste is transferred from one belt to another) means that it is rarely used in modern facilities.

===Roller grate===

The roller grate design consists of a perforated roller that traverses the width of the grate area. Several rollers are installed in series which rolls or tumbles the material forward, towards the ash discharge.

==Incineration Temperature, Residence Time and Oxygen Content==

Incinerators are designed and operated to ensure good burnout of the combustion gases. This is achieved by maintaining the gases at a maximum temperature for a minimum residence time at a minimum oxygen level. Temperature values typically range between 850°C to 1 100°C for at least two seconds at a minimum oxygen level of 6%. Higher temperatures can be associated with hazardous waste. The carbon monoxide content of the flue gases is a main indicator of the quality of combustion.

==References==

@@ Line 59: / Line 59: @@
 *Mixing of flue gases
+===Auxiliary Burners===
+Auxiliary burners are used at start up to heat the furnace to a required temperature before the waste is introduced. If the temperature falls below the desired value during operation, the burners are switched on automatically. The burners are utilised for shutdown to maintain the furnace temperature and ensure there is no unburnt waste left in the furnace.
+==Different Grate Types==
+The incineration grate can be categorised generally by feeder principles: continuous (roller and chain grates) and discontinuous (push grates). Grate systems can also be characterised by the way waste is conveyed through zones in the combustion chamber. Each must fulfil requirements regarding primary air feeding, conveying velocity, and mixing of waste. Other features include additional controls or a more robust construction to withstand the severe conditions in the combustion chamber.
+===Rocking grate===
+The rocking grate sections are placed across the width of the furnace. Alternative rows are mechanically pivoted or rocked to produce an upward and forward motion which advances and agitates the waste.
+===Reciprocating grate===
+The reciprocating grate sections span the width of the furnace and are stacked above each other. Alternative grate sections slide back and forth, while the adjustment sections remain fixed. Waste tumbles off the fixed portion and is agitated and mixed as it moves along the grate. Different variations of this type of grate exist, such as some with alternating fixed and moving sections, while others have combinations of several moving sections to each fixed section. In the latter case, the sections can either move together or at different times in the cycle.
+There are two main variations for reciprocating grates:
+====Reverse reciprocating grate====
+The grate bars move back and forth in the reverse direction to the flow of waste. The grate is flopped from the feed end to the ash discharge end and is comprised of fixed and moving grate steps.
+====Push forward grate====
+The grate bars form a series of many steps that move horizontally and push the waste in the direction of the ash discharge.
+===Travelling grate===
+The travelling grate type consists of a continuous metal belt conveyor interlocking linkage that move along the length of the furnace. The reduced potential to agitate the waste (mixing only occurs when waste is transferred from one belt to another) means that it is rarely used in modern facilities.
+===Roller grate===
+The roller grate design consists of a perforated roller that traverses the width of the grate area. Several rollers are installed in series which rolls or tumbles the material forward, towards the ash discharge.
+[[File:Different grate types.png|400px|left|Different grate types. All rights reserved.]]
+<br clear=all />
+==Incineration Temperature, Residence Time and Oxygen Content==
+Incinerators are designed and operated to ensure good burnout of the combustion gases. This is achieved by maintaining the gases at a maximum temperature for a minimum residence time at a minimum oxygen level. Temperature values typically range between 850°C to 1 100°C for at least two seconds at a minimum oxygen level of 6%. Higher temperatures can be associated with hazardous waste. The carbon monoxide content of the flue gases is a main indicator of the quality of combustion.
 ==References==
 <references />