JPH05296005A - Thermal power plant - Google Patents

Abstract

(57) [Summary] [Purpose] For a private thermal power plant installed in a steel mill, etc., while operating the boiler under constant load conditions when the power load in the plant increases or decreases in a short period, (EN) Provided is a thermal power plant capable of absorbing fluctuations in electric power load and improving thermal energy efficiency. [Structure] The rated internal pressure is set lower than the main steam pressure and higher than the mixed gas pressure of the steam turbine between the main steam pipe line connecting the boiler 1 and the mixed pressure steam turbine 2 and the intermediate stage of the turbine. Two-phase transformer steam accumulator 9
Connected to the boiler, while operating the boiler at a constant steam generation amount, according to the fluctuation pattern of the electric power load, when the load decreases, the surplus steam of the main steam is taken into the accumulator and stored,
The steam released from the accumulator when the load increases is introduced as a mixed pressure steam into the middle stage of the steam turbine to increase the turbine output and absorb a wide range of power load fluctuations.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal power plant suitable as a private power generation facility applied to a steel mill equipped with a rolling facility for iron manufacturing.

[0002]

2. Description of the Related Art In large-scale steel mills, there are many cases in which a private thermal power plant is installed in the plant and most of the electric power demand is covered by inexpensive electric power obtained from the private thermal power plant. In this case, in recent thermal power plants, a circulating fluidized bed type boiler is often used for the boiler from the viewpoint of pollution prevention. However, this circulating fluidized bed type boiler has a constant load condition ( Boiler steam generation amount is constant)
Since it is desirable to operate at a private plant, the above-mentioned private thermal power plant generates a base portion of the in-house power demand at the private plant and purchases power from the power company that corresponds to the increase / decrease in load. It is common to use it to cover.

On the other hand, in a conventional thermal power plant, as is well known, the turbine output steam control valve is adjusted to adjust the turbine output in response to fluctuations in power demand, and the boiler is adjusted in accordance with changes in the steam flow rate. The amount of steam generated is controlled. In this case, this method can be adequately used when the fluctuation speed of the power load is slow, but when the change speed of the load is fast, the time constant for the control response of the boiler is large. Is difficult to follow.

Therefore, in response to a rapid increase / decrease in load,
The unbalanced amount between the steam generation amount of the boiler and the steam swallowing amount of the steam turbine (for the fluctuation of the electric power load, the steam inflow amount is adjusted by controlling the inlet control valve of the steam turbine as described above) As a method of absorption, surplus steam at the time of load reduction is released directly to the atmosphere through the control valve,
Alternatively, in addition to the method of introducing excess steam into the condenser of the turbine to recover heat, the following load fluctuation absorption method has been conventionally known.

(1) A steam accumulator is branched and connected to a main steam line between a boiler and a steam turbine, and excess steam is guided to and stored in an accumulator when the power load decreases, and steam discharged from the accumulator when the load increases. It is supplied to the boiler feed water heater and deaerator, and the amount of extracted steam from the steam turbine is reduced by that amount and the turbine output is increased. (Japanese Patent Publication No. 59-28722)

(2) In addition to the steam accumulator described above, a small amount of hot water for auxiliary use is provided separately from the main steam turbine, or a steam turbine is installed in the plant, and hot water discharged from the accumulator when the electric power load increases. , Steam is supplied to the hot water for auxiliary and steam turbine for power generation or auxiliary power. (JP-A-58-107804)

[0007]

By the way, in a large-scale power consumer such as a steel mill, the private power generation plant installed in the plant as described above is operated under a constant load condition, and the fluctuation of the power demand in the plant is calculated by the power company. When purchasing electricity from the power plant, it is necessary to consider the peak load of power demand in the power plant and make a power purchase contract. Get high In view of this point, taking a steel mill equipped with a large rolling mill as an example, when examining the fluctuation of the electric power load inside the rolling mill during operation, as shown in FIG. 2 to
It has been confirmed that the maximum amplitude fluctuates greatly to about 30 MW in a short cycle of 5 minutes. Therefore, contrary to the past, the amount of power purchased from the power company is always constant,
If the private thermal power plant can be operated so as to absorb fluctuations in power demand in the plant, it will be possible to significantly reduce power purchase costs.Therefore, establish appropriate measures to absorb fluctuations in power load for private thermal power plants. Is strongly requested.

[0008] Therefore, the inventors examined the applicability of the above-mentioned conventional electric power load fluctuation absorbing systems (1) and (2) to a private thermal power plant installed in a steel mill. It turned out that there was a problem. That is, in the load fluctuation absorbing method (1), the steam accumulated in the accumulator is depressurized to a low pressure and used, so that a large amount of heat energy is lost and the heat energy utilization efficiency is low. Moreover, there is a time response delay from the start of steam supply from the accumulator to the feed water heater and deaerator until the steam turbine output increases.As this time constant is long, there is an interval of several minutes as described above. It is practically difficult to sufficiently follow the load fluctuation that changes in the cycle.

The load fluctuation absorbing method (2) described above is
In addition to increasing the facility cost to install an auxiliary turbine inside the plant, and increasing the time and effort required for its maintenance,
It is necessary for the auxiliary turbine to be started and stopped each time in accordance with the discharge of steam from the accumulator, and it is not possible to sufficiently follow the power load fluctuation that changes at intervals of several minutes like the rolling mill described above. Since the output of the auxiliary turbine is changed in the range of 0 to 100%, the efficiency is remarkably reduced particularly in the low load operation range.

The present invention has been made in view of the above points, and an object of the present invention is to provide a boiler for a private thermal power plant or the like in the above-mentioned steel mill when the power load in the plant increases or decreases in a short period. It is an object of the present invention to provide a thermal power plant capable of operating under a constant load condition, absorbing a wide range of power load fluctuations, improving thermal energy efficiency, and significantly reducing power purchase costs.

[0011]

According to the present invention, a main steam connecting a boiler and a steam turbine to a thermal power plant having a boiler, a mixed pressure steam turbine, and a generator as main equipment is provided by the present invention. A steam accumulator is connected between the pipeline and the intermediate section of the steam turbine to operate the boiler with a constant boiler steam generation amount, while accumulating excess steam of the main steam when the load decreases in accordance with the fluctuation pattern of the electric power load. It is achieved by increasing the turbine output by taking in and storing it in a steam turbine, and introducing the steam discharged from the accumulator when the load increases as mixed pressure steam into the intermediate fall of the steam turbine.

Here, it is preferable that the steam accumulator employs a two-phase transformer type accumulator in which the rated internal pressure is set lower than the main steam pressure and higher than the mixed pressure of the steam turbine. In addition, a steam control valve is connected to the inlet and outlet sides of the steam accumulator to control the main steam inflow into the accumulator and the mixed pressure steam discharge from the accumulator in accordance with the fluctuation pattern of the electric power load. There are some embodiments.

[0013]

In the above, the boiler is operated with a constant steam generation amount during the operation of the power plant. Then, in accordance with the increase / decrease fluctuation pattern of the electric power load due to the operation of on-site facilities (rolling mills, etc.), when the electric power load decreases, a part of the main steam is taken into the steam accumulator from the main steam pipeline and stored. On the other hand, when the electric power load starts to increase, the intake of the main steam into the accumulator is cut off, and the steam discharged from the accumulator is introduced as a mixed pressure steam into the middle paragraph of the steam turbine. Increase the output of the steam turbine.

As a result, the steam accumulator absorbs a wide range of increase / decrease in the electric power load in a short period while operating the boiler with a constant steam generation amount, and the turbine output is increased / decreased according to the electric power load change. You can Moreover, since the heat energy accumulated in the accumulator is used at high steam pressure and temperature, there is little loss of heat energy, and the steam discharged from the accumulator is directly supplied to the mixed pressure steam turbine. And high responsiveness is obtained.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. First, in FIG. 1, 1 is a boiler, 2 is a mixed pressure steam turbine, 3 is a generator, 4 is a condenser, 5 is a low-pressure side feed water heater, 6 is a deaerator, 7 is a water supply pump, and 8 is high pressure. It is a side feed water heater, and the main steam pipe line between the boiler 1 and the main steam control valve 2a of the mixed pressure type steam turbine 2 is branched from the pipe line and connected to an intermediate paragraph of the steam turbine 2. A steam accumulator 9 is newly added between the mixed pressure steam control valve 2b. This steam accumulator 9 is a two-phase transformer type accumulator whose rated internal pressure is set lower than the main steam pressure and higher than the mixed pressure of the steam turbine 2, and steam adjustment is performed on the inlet side and the outlet side respectively. The valves 10a and 10b are provided.

With such a configuration, the boiler 1 is operated under a constant load condition when the on-site facility is operating, the steam generated from the boiler 1 is sent to the turbine 2 to drive the turbine, and the electric power obtained by the generator 3 is supplied to the on-site facility. To do. Here, when the power load is reduced in accordance with the increase / decrease fluctuation pattern of the power load shown in FIG. 2, the main steam control valve 2a of the steam turbine 2 is throttled to reduce the turbine output, and on the other hand, to the outlet side of the accumulator 9. The pressure control valve 10a on the inlet side is opened while the connected control valve 10b is closed, and a part of the main steam is taken into the accumulator 9 as excess steam and stored. Then, when the power load next increases, the inlet side control valve 10a of the accumulator 9 is closed and the outlet side control valve 10b is closed.
Is opened to release steam obtained by re-evaporating hot water from the accumulator 9, and this steam is introduced into the intermediate paragraph of the steam turbine 2 through the mixed pressure steam control valve 2b to increase the turbine output together with the supply of main steam. .. As a result, the increase / decrease of the electric power load can be absorbed in a wide range while operating the boiler 1 under a constant load condition.

Here, FIG. 3 shows one cycle of the steam inflow and discharge operation patterns of the accumulator 9 corresponding to the power load fluctuation pattern shown in FIG. The amount of water injected in the figure represents the amount of water injected when the excess steam taken into the accumulator is reduced in temperature and converted into hot water, and the thermal energy of the steam is accumulated as sensible heat of the hot water. Regarding the specifications of the two-phase accumulator, for example, the volume ratio of the hot water part is 9
0%, the rated pressure in the vessel is 40 kg / cm ² a, which is slightly higher than the mixed pressure of the steam turbine (eg 31 kg / cm ² a), and the capacity is 90 m ³ , the steam accumulated in the vessel as shown in the figure. Can be released at a maximum of 70 t / h for 150 seconds, and by taking up a maximum of 54 t / h of main steam for 150 seconds in the next step, it becomes possible to return to the initial state.

The rated output of the turbine generator 3 is set to 75
If the main steam amount to be supplied to the turbine 2 from the boiler 1 at 000 kW is 250 t / h, in addition to the main steam amount of 250 t / h, steam of 70 t / h from the accumulator will be mixed pressure steam as turbine mixed pressure steam when the power load on the plant increases. The output of the turbine generator will increase to about 87,000 kW, and conversely 54t / h of the main steam will be generated when the power load decreases.
Is stored in the accumulator as excess steam,
The power of the turbine generator is reduced to about 57,000 KW.
The power difference of the turbine generator in these two states is about 30300.
Since it becomes kW, the fluctuation range of the power load shown in FIG.
Can cover W enough.

At the time of starting the thermal power plant, the steam generated in the boiler is introduced into the accumulator until it reaches the required steam pressure and temperature required for turbine operation. The turbine bypass device installed for the purpose of shortening the time can be omitted.

[0020]

As described above, according to the present invention, surplus steam is applied to a thermal power plant for private use installed in a rolling mill or the like of a steel mill in accordance with the fluctuation pattern of the power load in the plant, which increases and decreases in a short period. By accumulating in the accumulator and by supplying steam from the accumulator to the mixed pressure turbine, it is possible to absorb a wide range of fluctuations in the electric power load while operating the boiler at a constant steam generation amount. Moreover, since the heat energy of the steam accumulated in the accumulator is used at a high steam pressure and temperature, the loss of heat energy can be suppressed to a low level and the power load fluctuation of a short period can be sufficiently followed.

Further, according to the calculation of the economic effect based on the power purchase cost that can be saved by the present invention,
The capital investment of the steam accumulator, the steam control valve attached to it, and the control device can be recovered in about 3 years, and the contract fee and the usage fee paid to the electric power company can be significantly reduced compared to the conventional method mentioned above. it can.

[Brief description of drawings]

FIG. 1 is a system flow diagram of a thermal power plant according to an embodiment of the present invention.

FIG. 2 is a diagram showing a power load fluctuation pattern.

3 is a diagram showing one cycle of vapor inflow and outflow operations of the accumulator in FIG.

[Explanation of symbols]

 1 Boiler 2 Mixed Pressure Steam Turbine 3 Generator 9 Steam Accumulator 10a Inlet Steam Control Valve 10b Outlet Steam Control Valve

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasuhiro Nishizaki 1-1, Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa Fuji Electric Co., Ltd.

Claims (3)

[Claims] 1. A thermal power plant comprising a boiler, a mixed-pressure steam turbine, and a generator as main equipment. A steam accumulator is provided between a main steam pipeline connecting the boiler and the steam turbine and an intermediate stage of the steam turbine. Connect
While operating the boiler with a constant boiler steam generation amount, when the load decreases in accordance with the fluctuation pattern of the electric power load, excess steam of the main steam is taken into the accumulator and stored,
A thermal power plant characterized in that steam released from an accumulator when the load increases is introduced as mixed pressure steam into an intermediate stage of a steam turbine to increase turbine output. 2. The thermal power plant according to claim 1, wherein the steam accumulator is a two-phase transformer type accumulator in which the rated internal pressure is set lower than the main steam pressure and higher than the mixed pressure of the steam turbine. A thermal power plant characterized by the above. 3. The thermal power plant according to claim 1 or 2, wherein a steam control valve is connected to an inlet side and an outlet side of the steam accumulator, and a main steam inflow amount into the accumulator corresponding to an increase / decrease fluctuation pattern of an electric power load. , And a thermal power plant characterized by controlling the amount of mixed pressure steam discharged from an accumulator.