JPH08166109A - Pressurized fluidized bed plant - Google Patents

Abstract

PURPOSE: To achieve higher efficiency by providing a control valve on bypass piping for bypassing compressed air to an port of an air compressor to decrease an Nox generation quantity while wasting no heat value. CONSTITUTION: After the removal of dust with a ceramic filter 7, a high temperature and high pressure gas generated by a pressurized fluidized bed boiler 2 turns a gas turbine 3 to convert heat energy to mechanical energy and the gas with the pressure thereof approaching atmospheric pressure and with the temperature lowered undergoes a heat exchange with water and a steam system by a stack gas cooler 5 to be discharged from a stack 12. The air pressurized at an outlet of an air compressor 4 is recirculated to an inlet or an outlet of an air filter 15 to mix through an air control valve 13 and pressurized with the air compressor 4 via an IGV. Thus, the temperature of the air introduced into the compressor passing through the IGV rises to allow reduction in the mass of the air to be supplied to the pressurized fluidized bed boiler thereby enabling the supplying of the amount of air to match a load by recirculation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressurized fluidized bed plant composed of a pressurized fluidized bed boiler, a gas turbine, a generator, etc., and particularly, it is possible to improve the operability when the plant load changes. Pressure fluidized bed plant.

[0002]

2. Description of the Related Art A combined plant is generally composed of a gas turbine, a steam turbine and an exhaust heat recovery boiler. The exhaust gas from the gas turbine is used as a heat source to drive the steam turbine with steam generated in the exhaust heat recovery boiler. In this combined plant, a pressurized fluidized bed boiler that also serves as a combustor of a gas turbine is referred to as a pressurized fluidized bed plant.

This pressurized fluidized bed plant is specifically constructed as follows. First, compressed air is obtained by an air compressor driven by a gas turbine, and this air is supplied to a pressurized fluidized bed boiler stored in a pressurized container. Fossil fuel such as coal as a fuel is supplied to a boiler and burned in a slurry or paste state kneaded with a liquid such as water or in a dry state. The hot pressurized gas generated by combustion passes through the dust remover and is supplied to the gas turbine to obtain an output. On the other hand, the steam generated in the pressurized fluidized bed boiler drives the steam turbine to obtain output also in the steam turbine as combined power generation. Generally, the output of the steam turbine is about 6 to 7 times the output of the gas turbine.

The air at the outlet of the air compressor is supplied to the pressurized fluidized bed boiler in normal operation, but as an operating method when the load changes, for example, the one described in JP-A-5-263611 is known. The pressurized fluidized bed plant described in Japanese Patent Laid-Open No. 5-263611 will be described with reference to FIGS. 7 and 8. 1 is a pressure vessel, 2 is a pressurized fluidized bed boiler, 3 is a gas turbine, and 4 is air compression. Machine, 5 is a stack gas cooler, 6 is a steam turbine, 7 is a ceramic filter, 8 is a coal feeder, 9 is a booster,
The compressed air is introduced into the pressurized fluidized bed boiler 2 by the air compressor 4 as high pressure air. Further, the pressurized fluidized bed boiler 2 is supplied with coal from the coal supply device 8 and combusted using high pressure air to obtain high temperature combustion gas. The hot combustion gas is supplied to the gas turbine 3 through the ceramic filter 7 and expanded,
The air compressor 4 and the generator 10 are driven. After that, the gas turbine exhaust gas exchanges heat with the feed water in the stack gas cooler 5, and finally becomes low-temperature gas turbine exhaust gas, which is released to the atmosphere. On the other hand, the high-temperature feed water heated by the stack gas cooler 5 is supplied to the pressurized fluidized bed boiler 2, and the combustion heat of coal in the pressurized fluidized bed boiler 2 produces high-temperature and high-pressure steam, which is sent to the steam turbine 6 and sent to the steam turbine 6. 6 is rotationally driven. Further, the expanded low temperature reheated steam is sent again to the pressurized fluidized bed boiler 2 to recover heat to be high temperature reheated steam, and then sent to the steam turbine again to rotate the steam turbine. The steam turbine 6 drives a generator 11,
Get electrical output. The steam that has worked in the steam turbine 6 becomes low-temperature low-pressure steam, which is heat-exchanged with seawater in the condenser and condensed to be condensed water. Condensed water is pressurized by a high pressure supply pump installed at the outlet of the condenser and sent to the stack gas cooler 5. Further, in the above-mentioned conventional apparatus, as means for controlling the air amount, as shown in FIGS. 7 and 8, the compressor outlet air has a bypass line to the gas turbine exhaust side or to the atmosphere discharge or the gas turbine inlet. .

[0005]

An air compressor driven by a gas turbine is an IGV (Inlet Gu
An air control mechanism called ide Vane) was installed in the air intake section at the compressor inlet, which controlled the air intake amount. Further, when the IGV alone is insufficient, the air intake amount is further reduced by making the stationary blade movable. This IGV operates when it is necessary to throttle down the amount of air at startup when it is sufficient to use a small amount of combustion air at a partial load, and controls the amount of air that is approximately proportional to the amount of coal input, or that is commensurate with the required amount at startup. However, if the air volume was reduced too much, the air volume could not be reduced due to the contact with the urging area of the air compressor. In an air compressor connected to a general gas turbine, this throttle amount is maximum about 60% by adding a variable vane to the IGV (Fig. 9). Therefore, the following problems have arisen. That is, since the amount of air is excessive with respect to the required amount of combustion, the oxygen concentration during combustion is high and the generation of NOx increases. Further, since the limit power (for example, 60%) that the air compressor throttles by IGV is required even under a low load, the plant efficiency under a partial load is poor. In addition, the above-mentioned Japanese Unexamined Patent Publication
In the method of bypassing air by the method described in Japanese Patent Publication, although the amount of air supplied to the boiler is reduced by discarding it to the atmosphere side, the air that has been pressurized by the air compressor and has risen in temperature rises on the downstream side of heat. There was a problem that the efficiency was deteriorated by throwing it away.

Therefore, according to the present invention, by recirculating the air that has been compressed by the air compressor and whose temperature has risen to the inlet of the air compressor, the low load and the mass of air passing through the air compressor at the time of start are set to the target amount at the time of load and start. Accordingly, the amount of NOx generated is reduced by reducing the air supplied to the throttle fluidized bed boiler. Further, it is an object of the present invention to solve the above-mentioned conventional problems by recirculating the air whose temperature has been raised by an air compressor without wasting a heat amount and by improving the plant efficiency by feeding the heat into a fluidized bed boiler. .

[0007]

Therefore, the present invention provides an air compressor driven by a gas turbine, and a pressurized fluidized bed boiler that produces combustion gas by burning coal and air from the air compressor. , A gas turbine driven by combustion gas during normal operation, a steam turbine driven by steam generated by heat exchange between a stack gas cooler for exchanging heat from exhaust gas of the gas turbine to feed water, etc. and a stack gas cooler and a fluidized bed boiler, and A pressurized fluidized bed plant consisting of auxiliary equipment that constitutes the plant is equipped with a bypass pipe for bypassing compressed air to the air compressor inlet and a control valve provided on the same pipe. Is a means for.

[0008]

The plant load, the amount of air to the pressurized fluidized bed boiler, the plant efficiency and the amount of NOx generated are shown in FIGS. 3, 4 and 5.
Shown in FIG. 6 shows the operating characteristics with and without recirculation. By opening the recirculation valve as in the present invention, the hot air at the compressor outlet mixes with the air at the compressor inlet atmospheric temperature, which raises the intake air temperature. Since the characteristics of the air compressor are determined by the actual air volume flow rate, mixing the recirculated air increases the intake air temperature and reduces the intake air volume of the air compressor. As a result, the mass of air compressed by the compressor is reduced even with the same IGV opening, and as a result, the amount of air supplied to the pressurized fluidized bed boiler after subtracting the amount of recirculation is reduced. Further, as a result, the amount of gas supplied to the gas turbine is reduced and the system pressure is reduced, so that the margin for surging increases due to the characteristics of the compressor, and the operating margin further increases. As a result, the amount of NOx generated is drastically reduced, and the load on the denitration equipment installed downstream is lightened, and the denitration effect at the time of startup is produced. If it is used in the transitional period during load change, it can be operated outside the surging area and contribute to the improvement of load change speed.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 and FIG. 2 are plant system diagrams according to the embodiments of the present invention. In the figure, the pressurized fluidized bed plant mainly includes a pressurized vessel 1, a pressurized fluidized bed boiler 2, a gas turbine 3, an air compressor 4, a stack gas cooler 5, a steam turbine 6, a ceramic filter 7, and a coal supply device 8. It is configured as a device. Reference numeral 10 is a generator directly connected to the gas turbine, and functions as an electric motor when the output of the gas turbine is lower than the power of the air compressor at the time of starting. Further, 11 is a generator directly connected to the steam turbine. Air pressurized by the air compressor 4 is introduced into the pressurized fluidized bed boiler 2. Further, coal is supplied from the coal supply device 8 together with the air whose pressure is increased through the booster 9. When the coal is supplied by a wet method such as slurry, it is directly supplied into the fluidized bed. The pressurized fluidized bed boiler contains a fluidized material such as coal stone as a bed material to form a fluidized bed. A tube for generating or pressurizing steam is contained in the fluidized bed, and the generated steam drives the steam turbine 6. The high temperature and high pressure gas generated in the pressurized fluidized bed boiler 2 is dedusted by the ceramic filter 7 and then the gas turbine is rotated to convert thermal energy into mechanical energy so that the pressure becomes close to the atmospheric pressure and the temperature becomes low. The gas exchanges heat with the water and steam systems in the stack gas cooler 5 and is discharged from the chimney 12. The compressed air at the outlet of the air compressor is controlled by the air control valve 1
After being recirculated through 3 to the inlet or outlet of the air filter 15 and mixed, it is pressurized by the air compressor 4 via the IGV. Although FIG. 1 shows an example in which the gas turbine starting method is based on frequency control of the generator, a gas turbine starting combustor 16 may be installed as shown in FIG. In the configuration shown in FIG. 2, the valve 18 of the line 17 is opened at the time of starting the gas turbine to partly branch the combustion air from the air compressor 4 and supply it to the combustion air of the combustor 16.

[0010]

As described in detail above, according to the present invention, the temperature of the air introduced into the compressor through the IGV is increased by circulating the air from the outlet of the air compressor to the air intake through the air control valve. Then, the relationship of the mass of air supplied to the pressurized fluidized bed boiler can be reduced as shown in FIG. 3, and the amount of air corresponding to the load can be supplied by recirculating. As a result of this, for example, the minimum load N
The result is that the amount of Ox generated is reduced by about 20%.
In addition, the relationship between load and efficiency is shown in Fig.
It leads to efficiency improvement of several% between% loads. In addition to a lower load, the combustion in the pressurized fluidized bed boiler has a higher oxygen concentration than the normal operation at the time of startup, that is, a state in which the amount of air is larger than the amount of coal input. Even at such start-up, the present invention recirculates air to the inlet of the air compressor to lower the operating pressure of the gas system and maintain the superficial velocity of the fluidized bed, while enabling operation with a low air amount. Become. Further, as an additional advantage, it is possible to obtain an excellent effect that the mixing port of the recirculated air according to the present invention can also serve as the prevention of freezing of the air filter installed at the inlet of the air compressor.

[Brief description of drawings]

FIG. 1 is a plant system diagram of the present invention.

FIG. 2 is a plant system diagram of another embodiment of the present invention.

FIG. 3 is a diagram showing plant load and the amount of air to a fluidized bed boiler.

FIG. 4 is a diagram showing plant load and plant efficiency.

FIG. 5 is a diagram showing plant load and NOx generation amount.

FIG. 6 is a diagram showing operating characteristics of a compressor.

FIG. 7 is a plant system diagram according to a conventional technique.

FIG. 8 is a plant system diagram according to a conventional technique.

FIG. 9 is a diagram of the number of throttle stages and the amount of air.

[Explanation of symbols]

 1 Pressurized Container 2 Pressurized Fluidized Bed Boiler 3 Gas Turbine 4 Air Compressor 5 Stark Gas Cooler 6 Steam Turbine 7 Ceramic Filter 8 Coal Supply Device 9 Booster 10, 11 Generator 13 Air Control Valve

Claims (1)

[Claims] 1. An air compressor driven by a gas turbine, a pressurized fluidized bed boiler that generates combustion gas by burning coal and air from the air compressor, and a combustion gas driven during normal operation. It consists of a gas turbine, a stack gas cooler for exchanging heat from the exhaust gas of the gas turbine to feed water, etc., and a steam turbine driven by steam generated by heat exchange between the stack gas cooler and a fluidized bed boiler, and auxiliary equipment that constitutes a plant. A pressurized fluidized bed plant comprising a bypass pipe for bypassing compressed air to an air compressor inlet and a control valve provided on the pipe.