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59 Cards in this Set
- Front
- Back
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What is the purpose of a bridge wall? |
-Keep the fuel bed in place on the grates -Deflect the products of combustion against heating surfaces |
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What is the purpose of grates? |
-Support the fuel bed -Admit air into the furnace |
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What prevents grates from burning up? |
-Incoming air carrying heat away from the grates -Ash providing a barrier between the grates and combustion. |
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What is a chain grate stoker? |
Employs an endless chain which is constructed to form a support for the fuel. |
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What is a travelling grate stoker? |
Employs an endless chain, but differs from a chain grate stoker in that it carries small grate bars which support the fuel bed. |
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What determines the air opening in a chain and travelling grate stoker? |
The type of coal being burned |
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How is coal fed into a chain and travelling grate stoker? |
By gravity hopper located in the front of the furnace |
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How is the depth of the fuel bed controlled on a chain and travelling grate stoker? |
A hand adjusted gate. |
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How is the speed of the chain controlled on a chain and travelling grate stoker? |
A variable speed drive attached to the front sprockets of the chain. |
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What determines the speed of the chain in a chain and travelling grate stoker? |
Combustion control automatically regulates the speed of the grate to maintain steam pressure. |
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What are arches installed? |
-Protect the boiler from the direct heat of the furnace. -Direct the products of combustion along desired path. |
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What are clinkers? |
Clinkers are formed when hot ash adheres to the walls of the furnace. |
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How is clinker formation mitigated? |
Installation of water backs (clinker chills) |
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What are Water Backs (Clinker Chills)? |
Tubing used to cool the furnace walls using either low pressure water or connected to the boiler to be used as part of the heating surface. These tubes help to mitigate the formation of clinkers. |
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What coals are used on travelling and chain grate stokers? |
Non-caking, free burning coal. |
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What does tempering coal refer to? |
Adding water to the coal |
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When would it be necessary to temper coal? |
-When the coal is dry -Contains a high percentage of coke -Has a tendency to coke during combustion |
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In an underfeed stoker, how is coal moved from the hopper to the retort? |
-Reciprocating feeder block or ram -Power driven screw |
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What are tuyers? |
Air admitting ports. |
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What negative effects are there from running the hopper on an underfeed stoker empty or allowing the supply chute to clog? |
The fuel bed may begin to burn in the retort causing overheating of the tuyers. |
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What is cinder reinjection? |
Capture of unburned fuel material from flue gas and what collects in convection hoppers and reintroduction into the furnace for combustion. |
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What is the efficiency effect of cinder reinjection? |
3-5% |
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What feature of a travelling grate spreader stoker qualifies them for services with a fluctuating load? |
Fuel burned in suspension causes spreader stokers to respond quickly to load changes. |
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What is the purpose of the spreader stoker feeder? |
-Vary supply of coal to the furnace -Even fuel distribution on the grates. |
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What are the four parts of a spreader stoker feeder? |
-Feed Plate -Spill Plate -Rotor -Spill Plate Adjusting Screw |
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What are the 2 types of spreader stoker feeders? |
-Over-throw -Under-Throw |
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What is the purpose of pulverizing coal? |
Expose more surface area to oxygen |
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What is the maximum temperature the preheated air used for drying the surface moisture of coal can be? |
500F |
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What are the 2 types of pulverization systems? |
-Bin or Storage -Unit or Direct |
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What is the maximum outlet temperature for a unit pulverization system? |
180F |
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What is the maximum outlet temperature for a bin pulverization system? |
130F |
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Why is the maximum outlet temperature lower for a bin pulverization system than a unit system? |
To minimize the chance of a bin fire |
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What functions do primary air serve in a unit pulverization system? |
-Transports the fuel from the pulverizer to the burner -Provides initial air for combustion |
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What are the four types of pulverizers? |
-Impact -Ball Mill -Ball Race Mill -Bowl Mill |
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What are the 2 types of Bowl Mills? |
-Bowl rotates, rollers stationary -Rollers rotate, bowl stationary. |
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What are the 2 types of Mill Feeders? |
-Drum and Table -Drum with Pockets |
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What are the three basic methods of firing? |
-Vertical -Horizontal -Tangential |
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How is ash temperature controlled in a dry bottom furnace? |
One or more rows of tubes connected to the boiler circulation system create a cooling zone. The cooling effect changes the ash from a plastic or semi-liquid state to a dry ash. |
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Describe the firebox purge prior to lighting off burners. |
Furnace must be ventilated for at least 5 minutes with a minimum of 50% air flow. |
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What is combustion? |
Combustion is a chemical reaction chemical that occurs between a fuel and an oxidizing agent that produces energy, usually in the form of heat and light. |
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What are the "Limits of Flammability"? |
The points at which a fuel to air ratio is either too rich or too lean to support combustion. |
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What are the basic combustible elements when referring to furnace operation? |
-Carbon -Hydrogen -Sulfur (Although, sulfur is considered to be an impurity) |
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What are the 2 basic methods of firing commercial fuels? |
-Suspension burning -Fuel Bed Burning |
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What is ash? |
Residue from combustion and is composed of mineral impurities in the fuel |
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What are the four zones of a fuel bed? |
-Distillation -Reduction -Oxidation -Ash |
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What is happening in the distillation zone of a fuel bed? |
Volatile matter is distilled from the coal leaving coke. |
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What is happening in the oxidation zone? |
Coke is burned to CO2 when in presence of combustion air moving upwards through the grates. |
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What is happening in the reduction zone? |
CO2 from the oxidation zone passes across the coke in the reduction zone. The excess carbon encountered reduces the CO2 to CO which rises and is burned in the distillation zone. |
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What is the BTU content of 1 pound of coal? |
Approximately 14,500BTU |
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How much air is required to burn 1 pound of coal? |
In theory, 14. Actual practice, 17 |
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What general analysis are used to find the composition of coal? |
-Proximate Analysis -Ultimate Analysis |
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What results are reported from a proximate coal analysis? |
Volatile matter, fixed carbon, moisture, ash |
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What results are reported from an ultimate coal analysis? |
Nitrogen, oxygen, carbon, ash, sulfur, hydrogen (NOCASH) |
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What is excess air? |
Amount of air over and above that required for theoretical complete combustion of fuel. |
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What is caking coal? |
A property of the coal which causes it to pass from the solid state to a plastic state when heat is applied |
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What is a coal's grindability index? |
Reference number which indicates the ease with which a coal can be pulverized for suspension burning? |
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What are the 2 methods for determining grindability index? |
-Hargrove Method -Ball Mill Method
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Name the 6 types of coal. |
-Lignite -Sub Bituminous -Bituminous -Semi Bituminous -Semi Anthracite -Anthracite |
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How is the BTU content of coal determined? |
Bomb calorimeter |
