DE3204550A1 - Fluid Bed Combustion Process - Google Patents

Description

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Applicant: Coal Industry (Patents) Limited, Hobart House, Grosvenor Place, London, SW1X 7AE, England

Fluid bed combustion process DESCRIPTION

The invention relates to fluidized bed combustion processes.

Fluidized bed combustion has continued in recent years Spread due to their ability to

_on to ensure an increased heat transfer in the same way as conventional incineration devices. One of the problems associated with the use of fluidized bed combustion is controlling the combustion taking place within the bed over the range of necessary to achieve a variable output of a boiler to which the combustion is typically associated Fuel and air flow rates. If the temperature of the bed is monitored as a control parameter, changes in temperature can be used to generate error signals for controlling the fuel supply to the bed. However, the temperature of the bed does not respond promptly to changes in combustion conditions due to the thermal inertia of the bed material and its combustible contents, which is particularly evident when lump coal is consumed. The consequence of using this temperature as a control parameter is a sluggish response, which either reduces the permissible speed in changing the boiler output

output limited, or in a deviation from the preferred fuel to air operating ratio results.

In some of the fluidized-bed boiler systems built and operated by the applicant, a method for tracking the output was used developed. However, this method effectively requires three separate but interdependent control circuits. In particular, an increase or a decrease in the required heat output of the Boilers related to a falling or rising steam pressure in the case of a steam boiler, or to a falling or rising water temperature in the case of a hot water boiler. The changes in pressure or temperature parameters are monitored and vice versa A proportional control signal is fed to the signal box of the induction draft ventilation flap. In this way for example, a decrease in vapor pressure results in a movement of the induction draft fan flap to a more open position and vice versa.

Movements of the induction draft ventilation flap cause a change in pressure in the combustion chamber above the bed, which by one with the signal box of the ventilation flap for reinforced train connected control device is demonstrated. In this way, the flap will be reinforced for the Train moves automatically in order to restore the desired state of pressure in the combustion chamber.

The response speed of the interlocking for the flap for increased train is generally sufficiently high compared to the signal box for the induction train flap, to regulate the combustion chamber pressure during

to maintain the duration of the performance update. 35

The changes in the flap position for increased pull cause changes in the air flow rate for the bed material, making proportional changes in

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the vortex velocity, thereby increasing the amount of bed expansion relative to the depth of the static Bed is affected. For example, if there is an increase in the air flow rate, this is subject to Bed cools down for two reasons. First got there a larger proportion of air at ambient temperature through the bed material and removes additional heat, and secondly, through increased bed expansion, a larger surface area with the bed material, which cools the bed, is created brought into contact. Therefore, a bed temperature sensor connected to the coal feed system accommodates changes the bed cooling by introducing appropriate changes in the rate of coal feed to reduce the Bring bed temperature back to a predetermined value.

Although this control method is essentially a Maintaining constant bed temperature and free space pressure does not necessarily maintain it maintains a constant fuel to air ratio. In addition, it suffers from the above-mentioned thermal Indolence of the bed. Although the flap for the induction train and, subsequently, the flaps for the reinforced train can be moved quickly so that they can rapidly change the flow rates of exhaust gas and combustion air generate, the resulting rate of change in bed temperature is much slower. To- The maintenance of a constant fuel to air ratio depends largely on changes in fuel and air is dependent on the same velocities, With the aforementioned control method, it is necessary to counteract the speed of the movement of the fan flaps in such a way that that it is adapted to the speed of response of the bed temperature. This is especially important with a decreasing output, if a rapid decrease in the combustion air flow rate is an un-

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Desired migration to fuel-rich operating conditions could cause within the fluidized bed. Another disadvantage of such a control method can be that that if, due to the cooling of the bed by expansion of the same, a larger heat exchange surface area immersed in the bed or in some other way, for example when feeding material into the bed, the -

Limitation of the bed temperature to a predetermined value

limits the range of power changes that can be followed as temperature affects burn rates at a given concentration of the coal bed and air inlet speed.

In addition, the bed temperature as a parameter only reflects the combustion that takes place in the bed and the. Share of the boiler output power that results from this combustion. However, it shows nothing on with respect to other components of boiler output such as those that rely on heat transfer from the free space above the bed as well as to those passing through the usual heat exchange smoke ducts Exhaust gases are based.

It is an object of the invention to provide a method of controlling fluidized bed combustion which utilizes the Improved the effectiveness of the control of the combustion process.

Accordingly, the invention provides a method for controlling fluidized bed combustion, wherein a fluidized bed combustion chamber contains a fluidized bed of granular material with an overlying one Free space, and where the temperature of this free space is monitored and as a control element for controlling incineration inside the bed.

It has been found that between the temperature of the Bed material and the temperature of the free space, i.e. the B temperature of the gas within the free space, a relationship consists. Indeed, the temperature of the free space gives quick and more accurate feedback on this the state of the combustion taking place inside and above the bed and thus gives a more effective one J.0 control parameters.

The temperature of the free space can be used to control the rate of fuel supply to the fluidized bed, thereby controlling the bed temperature and thus the combustion process. For example, changing the air supply to the fluidized bed results in a very large change in the temperature of the bed faster change in the temperature of the free space. This rapid response is due to the effects of the fuel-to-air ratio, which creates a change in the combustion taking place in the free space. A change in coal feed in response to a change in free space temperature quickly corrects the air-to-fuel ratio. The exhaust gases from the free space have a lower thermal inertia than those from the bed and this results in the faster response mentioned. Therefore, more steady operation can be achieved, which allows operation closer to the operating limit. In this example, the bed temperature is not controlled so that it remains at a predetermined value, but the bed temperature may be within a temperature range, for example, vary from 750 to 900 ⁰ C. The invention also includes the step of monitoring both bed temperature and free space temperature to measure the differential temperature. This difference is a function of various operating parameters, but mainly the air to fuel ratio. Thus, by measuring this temperature difference, information

of the kind obtained from an O ^ or CCL exhaust gas analyzer can be made available without the expense and complexity of such apparatus.

The invention thus together creates the possibility of an inexpensive control method for fluidized bed combustion with the advantages of air-to-fuel monitoring.

Claims (5)

B4TENMNIMLTE TBRQSE ^DKi BROSE Graduate engineer D-8023 Munich-PuIIach. Wiener Str. 2; TeS. φβδ) 7 ^ "3" 0 71: TelexjfciJJ ^ .bros d; Gables: -.Patentibus »Munich j APPROPRIATE File number: P 32 04 550.6 Applicant: Coal Industry (Patents) Limited Case 4287 day: March 15, 198.2 Your ref: Date: Re-3U NEW CLAIM 1 Method for monitoring fluidized bed combustion in a fluidized bed combustion chamber with a fluidized bed made of granular material with a free space above, characterized in that the temperature of the free space is monitored and that the monitored temperature is used as a control element used to control combustion within the bed. D-8023 Munich-Pullach. Wiener Str. 2; Part «89} 7 * θβ 30» 1 * Telex 5312147 Vros J *; tables: "Patentibus" Munich Applicant: Coal Industry (Patents) Limited, Hobart House, Grosvenor Place, London, SW1X 7AE, England Your reference: Your ref .: Case 4287 rag: February 9, 1982 Date: Re / hÖ PATENT CLAIMS ee · ecttjcffffg Tn a swirl bed combustion chamber mvt __ ^ eJ-fr € mWi swirl bed made of granular material aJ ^ j »4-t""'eTnem overlying free space, dadu ^ fii marked that the dj_e ^ Ji-fcrB ~ fwwehte temperature as a control egg emervt ^ tHiT ^ control the combustion within the bed. »eo- J 2. The method according to claim 1, characterized in that the temperature of the free space is used as a control parameter for controlling the speed of the fuel supply to the fluidized bed. 3. The method according to claim 1, characterized in that the air to fuel ratio is controlled by using the temperature of the free space as a control parameter will. 4. The method according to claim 1, characterized in that that the temperature of the fluidized bed is monitored. 5. The method according to claim 4, characterized in that that the difference between the temperature of the bed and the temperature of the free space is monitored and that the difference is used to control the combustion within the fluidized bed.