Grate: Difference between revisions

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[[Category:Technologies & Solutions]]

[[Grate]]-type [[Incineration|incinerators]] are suitable for large irregular-shaped [[Waste|wastes]], which can be supported on a stationary or moving alloy [[Grate]] that allows air to pass through from underneath into the [[Waste|waste]]. The primary furnace is followed by a secondary [[Combustion|combustion]] chamber, where additional air and fuel are added, to ensure complete destruction of all toxic emissions. These types of [[Incineration|incinerators]] are widely used for the [[Incineration|incineration]] of solid mixed [[Municipal Solid Waste|municipal waste]] ([[MSW]]), but can also be applied to [[Sewage Sludge|sewage sludge]], [[Clinical Waste|clinical waste]], and [[Commercial and Industrial Waste|commercial and industrial waste]] (C&I)<ref name="ref1">[https://eippcb.jrc.ec.europa.eu/sites/default/files/2020-01/JRC118637_WI_Bref_2019_published_0.pdf Best Available Techniques (BAT) Reference Document for Waste Incineration]</ref>. They generally have limited application for [[Hazardous Waste|hazardous waste]] [[Incineration|incineration]] due to the high temperatures required in the chamber which could have adverse effects the structure of the [[Grate]]<ref>[https://www.sciencedirect.com/science/article/pii/B9780123736239500034 Sustainable Industrial Design and Waste Management]</ref>.

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===Incineration Grate===

The roles of the [[Incineration|incineration]] [[Grate]] include loosening the materials to be [[Incineration|incinerated]] and transporting the materials to be [[Incineration|incinerated]] in the furnace. The [[Grate]] requires good distribution of the [[Incineration|incineration]] air into the furnace. A primary air blower forces [[Incineration|incineration]] air through the small [[Grate]] layer openings into the fuel layer. More air is usually added above the [[Waste|waste]] bed to complete [[Combustion|combustion]]. The residence time of the [[Waste|wastes]] on the [[Grate~~|grates~~]] generally ~~does not exceed more than~~ 60 minutes.

The roles of the [[Incineration|incineration]] [[Grate]] include loosening the materials to be [[Incineration|incinerated]] and transporting the materials to be [[Incineration|incinerated]] in the furnace. The [[Grate]] requires good distribution of the [[Incineration|incineration]] air into the furnace. A primary air blower forces [[Incineration|incineration]] air through the small [[Grate]] layer openings into the fuel layer. More air is usually added above the [[Waste|waste]] bed to complete [[Combustion|combustion]]. The residence time of the [[Waste|wastes]] on the [[Grate]] is generally around 60 minutes.

Some fine material (referred to as siftings/riddling) may fall through the [[Grate]] which gets recovered in the [[Fly Ash|bottom ash]] remover or is recovered separately. It can be recycled to the [[Grate]] for repeated [[Incineration|incineration]] or removed for disposal. If the siftings are recirculated in the hopper, care is taken not to ignite the [[Waste|waste]] in the hopper.

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The following characteristics influence the design of the [[Incineration|incineration]] chamber:

*Shape and size of the [[Incineration|incineration]] [[Grate]]

*Sufficient residence time for the [[Flue ~~Gases~~|flue gases]] in the hot furnace

*Sufficient residence time for the [[Flue Gas|flue gases]] in the hot furnace

*Partial cooling of [[Flue ~~Gases~~|flue gases]] by the injection of secondary air

*Partial cooling of [[Flue Gas|flue gases]] by the injection of secondary air

[[File:Different furnace designs with differing direction of the flue gas and the waste flow.png|400px|right|Different furnace designs with differing direction of the flue gas and the waste flow. All rights reserved.]]

The detailed design of a [[Combustion|combustion]] chamber is usually linked to the [[Grate]] type. Its precise design demands certain compromises as the process requirements change with the fuel characteristics. In general, three different designs can be distinguished based on the flow direction of the [[Flue ~~Gases~~|flue gases]] in relation to the [[Waste|waste]] flow: unidirectional current, counter-current and medium current.

The detailed design of a [[Combustion|combustion]] chamber is usually linked to the [[Grate]] type. Its precise design demands certain compromises as the process requirements change with the fuel characteristics. In general, three different designs can be distinguished based on the flow direction of the [[Flue Gas|flue gases]] in relation to the [[Waste|waste]] flow: unidirectional current, counter-current and medium current.

===Incineration Air Feeding===

Air is added at through various inlets in the [[Combustion|combustion]] chamber which is usually described as primary or secondary. Tertiary air and recirculated [[Flue ~~Gases~~|flue gases]] are used as well but are less common. Primary air is blown into areas below the [[Grate]] which cools the grate bar and caries oxygen into the [[Incineration|incineration]] bed. The secondary air is blown into the chamber to ensure complete [[Incineration|incineration]] of any [[Waste|waste]] left and intensive mixing of [[Flue ~~Gases~~|flue gases]].

Air is added at through various inlets in the [[Combustion|combustion]] chamber which is usually described as primary or secondary. Tertiary air and recirculated [[Flue Gas|flue gases]] are used as well but are less common. Primary air is blown into areas below the [[Grate]] which cools the grate bar and caries oxygen into the [[Incineration|incineration]] bed. The secondary air is blown into the chamber to ensure complete [[Incineration|incineration]] of any [[Waste|waste]] left and intensive mixing of [[Flue Gas|flue gases]].

The main roles of the [[Incineration|incineration]] air:

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*Cooling

*Avoidance of slag formation

*Mixing of [[Flue ~~Gases~~|flue gases]]

*Mixing of [[Flue Gas|flue gases]]

===Auxiliary Burners===

Auxiliary burners are used at start up to heat the furnace to a required temperature before the [[Waste|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|waste]] left in the furnace.

Auxiliary burners are used at start up to heat the furnace to a required temperature before the [[Waste|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|waste]] left in the furnace<ref name="ref1" />.

==Different Grate Types==

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There are two main variations for reciprocating [[Grate|Grates]]:

====Reverse reciprocating grate====

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

The [[Grate]] bars move back and forth in the reverse direction to the flow of [[Waste|waste]]. The [[Grate]] is sloped 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|waste]] in the direction of the [[Fly Ash|ash]] discharge.

===Travelling grate===

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===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 [[Fly Ash|ash]] discharge.

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 [[Fly Ash|ash]] discharge<ref name="ref1" />.

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

[[Incineration|Incinerators]] are designed and operated to ensure good burnout of the [[Combustion|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|hazardous waste]]. The carbon monoxide content of the [[Flue Gas|flue gases]] is a main indicator of the quality of [[Combustion|combustion]].

[[Incineration|Incinerators]] are designed and operated to ensure good burnout of the [[Combustion|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 1100°C for at least two seconds at a minimum oxygen level of 6%. Higher temperatures can be associated with [[Hazardous Waste|hazardous waste]]. The carbon monoxide content of the [[Flue Gas|flue gases]] is a main indicator of the quality of [[Combustion|combustion]]<ref name="ref1" />.

==References==

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+[[Category:Technologies & Solutions]]
 [[Grate]]-type [[Incineration|incinerators]] are suitable for large irregular-shaped [[Waste|wastes]], which can be supported on a stationary or moving alloy [[Grate]] that allows air to pass through from underneath into the [[Waste|waste]]. The primary furnace is followed by a secondary [[Combustion|combustion]] chamber, where additional air and fuel are added, to ensure complete destruction of all toxic emissions. These types of [[Incineration|incinerators]] are widely used for the [[Incineration|incineration]] of solid mixed [[Municipal Solid Waste|municipal waste]] ([[MSW]]), but can also be applied to [[Sewage Sludge|sewage sludge]], [[Clinical Waste|clinical waste]], and [[Commercial and Industrial Waste|commercial and industrial waste]] (C&I)<ref name="ref1">[https://eippcb.jrc.ec.europa.eu/sites/default/files/2020-01/JRC118637_WI_Bref_2019_published_0.pdf Best Available Techniques (BAT) Reference Document for Waste Incineration]</ref>. They generally have limited application for [[Hazardous Waste|hazardous waste]] [[Incineration|incineration]] due to the high temperatures required in the chamber which could have adverse effects the structure of the [[Grate]]<ref>[https://www.sciencedirect.com/science/article/pii/B9780123736239500034 Sustainable Industrial Design and Waste Management]</ref>.
@@ Line 24: / Line 25: @@
 ===Incineration Grate===
-The roles of the [[Incineration|incineration]] [[Grate]] include loosening the materials to be [[Incineration|incinerated]] and transporting the materials to be [[Incineration|incinerated]] in the furnace. The [[Grate]] requires good distribution of the [[Incineration|incineration]] air into the furnace. A primary air blower forces [[Incineration|incineration]] air through the small [[Grate]] layer openings into the fuel layer. More air is usually added above the [[Waste|waste]] bed to complete [[Combustion|combustion]]. The residence time of the [[Waste|wastes]] on the [[Grate|grates]] generally does not exceed more than 60 minutes.
+The roles of the [[Incineration|incineration]] [[Grate]] include loosening the materials to be [[Incineration|incinerated]] and transporting the materials to be [[Incineration|incinerated]] in the furnace. The [[Grate]] requires good distribution of the [[Incineration|incineration]] air into the furnace. A primary air blower forces [[Incineration|incineration]] air through the small [[Grate]] layer openings into the fuel layer. More air is usually added above the [[Waste|waste]] bed to complete [[Combustion|combustion]]. The residence time of the [[Waste|wastes]] on the [[Grate]] is generally around 60 minutes.
 Some fine material (referred to as siftings/riddling) may fall through the [[Grate]] which gets recovered in the [[Fly Ash|bottom ash]] remover or is recovered separately. It can be recycled to the [[Grate]] for repeated [[Incineration|incineration]] or removed for disposal. If the siftings are recirculated in the hopper, care is taken not to ignite the [[Waste|waste]] in the hopper.
@@ Line 42: / Line 43: @@
 The following characteristics influence the design of the [[Incineration|incineration]] chamber:
 *Shape and size of the [[Incineration|incineration]] [[Grate]]
-*Sufficient residence time for the [[Flue Gases|flue gases]] in the hot furnace
+*Sufficient residence time for the [[Flue Gas|flue gases]] in the hot furnace
-*Partial cooling of [[Flue Gases|flue gases]] by the injection of secondary air
+*Partial cooling of [[Flue Gas|flue gases]] by the injection of secondary air
 <br clear=all />
 [[File:Different furnace designs with differing direction of the flue gas and the waste flow.png|400px|right|Different furnace designs with differing direction of the flue gas and the waste flow. All rights reserved.]]
-The detailed design of a [[Combustion|combustion]] chamber is usually linked to the [[Grate]] type. Its precise design demands certain compromises as the process requirements change with the fuel characteristics. In general, three different designs can be distinguished based on the flow direction of the [[Flue Gases|flue gases]] in relation to the [[Waste|waste]] flow: unidirectional current, counter-current and medium current.
+The detailed design of a [[Combustion|combustion]] chamber is usually linked to the [[Grate]] type. Its precise design demands certain compromises as the process requirements change with the fuel characteristics. In general, three different designs can be distinguished based on the flow direction of the [[Flue Gas|flue gases]] in relation to the [[Waste|waste]] flow: unidirectional current, counter-current and medium current.
 <br clear=all />
 ===Incineration Air Feeding===
-Air is added at through various inlets in the [[Combustion|combustion]] chamber which is usually described as primary or secondary. Tertiary air and recirculated [[Flue Gases|flue gases]] are used as well but are less common. Primary air is blown into areas below the [[Grate]] which cools the grate bar and caries oxygen into the [[Incineration|incineration]] bed. The secondary air is blown into the chamber to ensure complete [[Incineration|incineration]] of any [[Waste|waste]] left and intensive mixing of [[Flue Gases|flue gases]].
+Air is added at through various inlets in the [[Combustion|combustion]] chamber which is usually described as primary or secondary. Tertiary air and recirculated [[Flue Gas|flue gases]] are used as well but are less common. Primary air is blown into areas below the [[Grate]] which cools the grate bar and caries oxygen into the [[Incineration|incineration]] bed. The secondary air is blown into the chamber to ensure complete [[Incineration|incineration]] of any [[Waste|waste]] left and intensive mixing of [[Flue Gas|flue gases]].
 The main roles of the [[Incineration|incineration]] air:
@@ Line 57: / Line 58: @@
 *Cooling
 *Avoidance of slag formation
-*Mixing of [[Flue Gases|flue gases]]
+*Mixing of [[Flue Gas|flue gases]]
 ===Auxiliary Burners===
-Auxiliary burners are used at start up to heat the furnace to a required temperature before the [[Waste|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|waste]] left in the furnace.
+Auxiliary burners are used at start up to heat the furnace to a required temperature before the [[Waste|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|waste]] left in the furnace<ref name="ref1" />.
 ==Different Grate Types==
@@ Line 72: / Line 73: @@
 There are two main variations for reciprocating [[Grate|Grates]]:
 ====Reverse reciprocating grate====
-The [[Grate]] bars move back and forth in the reverse direction to the flow of [[Waste|waste]]. The [[Grate]] is flopped from the feed end to the ash discharge end and is comprised of fixed and moving grate steps.
+[[File:Reverse feed grate.png|200px|right|Reverse feed grate. All rights reserved.]]
+The [[Grate]] bars move back and forth in the reverse direction to the flow of [[Waste|waste]]. The [[Grate]] is sloped from the feed end to the ash discharge end and is comprised of fixed and moving grate steps.
+<br clear=all />
 ====Push forward grate====
+[[File:Forward feed grate.png|200px|right|Forward feed grate. All rights reserved.]]
 The [[Grate]] bars form a series of many steps that move horizontally and push the [[Waste|waste]] in the direction of the [[Fly Ash|ash]] discharge.
+<br clear=all />
 ===Travelling grate===
@@ Line 80: / Line 86: @@
 ===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 [[Fly Ash|ash]] discharge.
+[[File:Roller grate.png|200px|right|Roller grate. All rights reserved.]]
+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 [[Fly Ash|ash]] discharge<ref name="ref1" />.
+<br clear=all />
 ==Incineration Temperature, Residence Time and Oxygen Content==
-[[Incineration|Incinerators]] are designed and operated to ensure good burnout of the [[Combustion|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|hazardous waste]]. The carbon monoxide content of the [[Flue Gas|flue gases]] is a main indicator of the quality of [[Combustion|combustion]].
+[[Incineration|Incinerators]] are designed and operated to ensure good burnout of the [[Combustion|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 1100°C for at least two seconds at a minimum oxygen level of 6%. Higher temperatures can be associated with [[Hazardous Waste|hazardous waste]]. The carbon monoxide content of the [[Flue Gas|flue gases]] is a main indicator of the quality of [[Combustion|combustion]]<ref name="ref1" />.
 ==References==
 <references />