Heating – Processes of heating or heater operation – Including apparatus purging – cleaning or accretion preventing
Patent
1994-11-30
1998-04-21
Bennett, Henry A.
Heating
Processes of heating or heater operation
Including apparatus purging, cleaning or accretion preventing
432 75, 122380, 122384, 122390, 110212, F24D 500, F28G 102
Patent
active
057411301
DESCRIPTION:
BRIEF SUMMARY
FIELD OF INVENTION
With different types of actual combustion and gasification processes there exists an increasing demand for quality and quantity gas analysis. Nitrogen oxides are at present the most exposed flue gas components, especially when considering tariff which has been introduced in Sweden for plants larger than 10 MW and with an annual energy production greater than 50 GWh.
These effect and energy limits, respectively, will most probably be reduced while at the same time greater demands will be made on the measurement of other types of flue gas components, i.e. CO and N.sub.2 O (laughing-gas).
The large majority of existing combustion systems are so designed that a minimum quantity of all unwanted flue gas components is very difficult to attain simultaneously. In other words "compromise agreements" e.g. high CO-concentrations--low NO-concentrations are unavoidable in these systems.
The fuel composition often varies from one operational condition to another, particularly with regard to different types of waste fuels and also wood fuels.
Examples of ash and/or slag enriched fuels comprise wood fuels, straw, waste such as industrial, municipal, hazardous and hospital waste and also hard coal, lignite, peat, lime sludge and black liquor. Also crematories and cement kilns are included in this category of combustion/gasification systems.
"Ash" is a term which designates an inorganic and unburnable substance which is originally within the fuel.
"Slag" is a term which designates "additives" of inorganic and unburnable substances, such as metals, ceramics, glass, stone etcetera. "Ash" is often considered contained within the term "slag".
Fuel price is another important parameter for optimization of flue gas or gas parameters. Sulphur content and to a certain degree also nitrogen content in the fuel are directly proportional to the emission level ahead of a flue gas cleaning system. This of course has the consequence that the fuel price becomes higher when i.e. the nitrogen content in the fuel is higher. Of course also the economical result is influenced by the market price and this will sometimes change quickly.
Trade in emission rights according to so called bubble models are systems which are expected to have a break-through on the market in the future.
The above parameters show a future need of flexible combustion/gasification systems which can be quickly adjusted to attain an optimal economical operation point on each occasion.
When using an optimization of this kind the perforated tubes in the combustion or gasification chamber are fed by a fluid comprising a gas or a liquid or possibly solid particles. Examples of gas are air, oxygen, oxygen-enriched air, flue gas, inert gas (CO.sub.2, N.sub.2 etc), fuel for reburning (LP-gas, natural gas etc) NO.sub.x reducing substances (NH.sub.3, urea etc) and steam with an optimal flow, pressure and temperature.
Examples of liquids are water, NH.sub.3, urea etc. Examples of solid particles are powder from biofuel including peat, coal and waste (plastic etc). These can be used as a reburning fuel.
Actual oxidizing agents, e.g. air, shall oxidize unburnt gases, e.g. CO, while reducing agents, e.g. NH.sub.3 or for example LP-gas, shall reduce for example NO at different occasions in a desired optimal degree.
The tube or the tubes is/are suitably positioned in the combustion/gasification plant to give an optimal effect.
In for example a grate fired boiler with "over combustion", where the air beneath the fuel makes the flue gas move upwards, the tube or tubes can be placed over the grate in connection with the first draught of the boiler. For a combustion process with so called "under combustion" the reverse will apply.
In for example a fluidized bed with variable pressure the tube or tubes can be positioned in the combustion chamber.
BACKGROUND ART
Today combustion/gasification of ash and slag enriched fuels takes place in a variety of different apparatus and plants in the form of kilns, furnaces etc with burners, grates, fluidized and/or bubbling beds etc.
On
REFERENCES:
patent: 884728 (1908-04-01), Gray
patent: 2225200 (1940-12-01), Ames
patent: 4883003 (1989-11-01), Hoskinson
patent: 5065472 (1991-11-01), Carpenter et al.
patent: 5197837 (1993-03-01), Brown
Hagstrom Ulf G.
Norelius Eric W.
Bennett Henry A.
Ecological Combustion i Stockholm AB
Lu Jiping
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