JPH05248603A - Reheater outlet steam temperature adjusting device - Google Patents

Abstract

PURPOSE:To facilitate adjustment of temperature of steam got out of a reheater and enable a high efficient operation of a plant to be carried out by a method wherein a secondary super heater and the reheater are arranged at a rear part of a furnace of a boiler and a flow passage bank for adjusting temperature of steam at an outlet port of the heater. CONSTITUTION:At a boiler in a thermoelectric power plant, main steam outputted from its secondary super heater is sent to high pressure turbine, steam of which work has been completed is returned back again to the boiler, reheated at the reheater 6 and 7, thereafter the steam is supplied to an intermediate pressure turbine and a low pressure turbine. In this case, the pipe arrangements of the reheater 6 and 7 are made such that a partition plate and a caster 53 are arranged in a main gas flow passage 51 and a bypassing flow passage 52 at about 25 to 50% height of the gas flow passage and then a cassette type buffle plate 54 acting as a flow passage bank which can be removably arranged is installed in the bypassing flow passage 52. In the case that some scales out of the pipes are dropped, a thermal collection of the secondary super heater is increased and then thermal collection at the reheater 6 and 7 is decreased, the fixing of the buffle plate 54 causes the coefficient of overall heat transmission of the reheater 6 and 7 to be increased and the temperature of steam at the outlet is increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reheater outlet steam temperature adjusting device which is provided at a rear part of a furnace of a boiler and adjusts an outlet steam temperature of a reheater. The slag on the outer surface of the vessel fell off,
The present invention relates to a reheater outlet steam temperature control device suitable for recovering the steam temperature when the reheat steam temperature does not reach a predetermined value due to a change in heat absorption amount.

[0002]

2. Description of the Related Art In recent years, a thermal power plant was constructed as a large-capacity base load thermal power at the time of construction because of the relationship between the stable supply of electric power from a nuclear power plant and the demand for electric power. Repeat Daily Start
There are many units that are forced to operate Stop (DSS).

FIG. 3 shows a structural example of a boiler of a thermal power plant. As shown in FIG. 3, the main steam heated to a predetermined temperature by the secondary superheater 2 of the boiler 1 is sent to the high-pressure turbine 4 via the main steam pipe 3. The main steam is consumed as rotational energy in the high-pressure turbine 4, decompressed and cooled, and then returned to the boiler 1 through the low-temperature reheat steam pipe 5. Then, after being reheated by the reheaters 6 and 7, it is sent to the intermediate pressure turbine 9 and the low pressure turbine 10 through the high temperature reheat steam pipe 8 to rotate the turbines 9 and 10. By recovering the heat in this way, the efficiency of the plant is improved.

The steam temperature at the outlets of the reheaters 6, 7 is
Depending on the strength of the metal material forming the reheaters 6 and 7 and the balance with the high-pressure turbine 4 side, the temperature is controlled in advance to a predetermined temperature, for example, around 550 to 570 ° C. Then, in order to prevent the temperature from rising, the reheat steam temperature reducer (reducer) 11 provided in the low temperature reheat steam pipe 5 is connected to the spray valve 1
It is controlled by injecting spray water via 2 When the temperature is low, heat is absorbed by the convection heat transfer in the reheaters 6 and 7. Therefore, the exhaust gas discharged from the outlet of the economizer 13 is recirculated into the boiler 1 by the exhaust gas recirculation fan 14. That is, it is common practice to increase the flow rate of the convection heat transfer section to increase the amount of heat exchange.

In this case, the plant efficiency is lowered even if the amount of spray water for controlling the steam temperature is too large, and the plant efficiency is lowered even if the steam temperature does not reach a predetermined value. That is, the steam temperature at the outlets of the reheaters 6 and 7 greatly affects the operation efficiency of the plant. Therefore, in order to maintain high plant efficiency, a damper 16 has been conventionally provided in the exhaust gas pipe 15 from the economizer 13 to adjust the exhaust gas circulation flow rate and control not only the rated load but also the partial load operation. It was

On the other hand, in determining the heat transfer area in the boiler 1 using such a fossil fuel, impurities in the fuel such as ash, vanadium, sodium, SO _{4 in the} heavy oil are formed on the outer surface of the heat transfer tube. Is determined on the assumption that the heat exchange rate will be adhered to a certain thickness over time and the heat exchange rate will be hindered, and the coefficient is a value obtained empirically. This change over time is also collectively referred to as seasoning. In general, the oil-fired unit reaches the planned value in 6 months at the earliest and 1.5 years in the late unit.

The heat transfer area and the heat collection are determined in such a manner that the secondary superheater 2 and the reheaters 6 and 7 interfere with each other to balance the heat. For example, the secondary superheater 2 compared to the plan
If the heat collection is high, the exhaust gas temperature at the outlet of the secondary superheater 2 decreases, and the heat collection in the reheaters 6 and 7 decreases. As a result, the outlet steam temperature does not reach the planned value, and the amount of spray water at the inlet of the reheater becomes excessive because it exceeds the planned value. That is, there is a mutual interference relationship.

Further, in recent years, in order to protect the environment, particularly to reduce nitrogen oxides in exhaust gas, the exhaust gas pipe 1 originally provided for controlling the steam temperature at the outlets of the reheaters 6 and 7.
The recirculated gas in No. 5 is mixed in the combustion air to reduce nitrogen oxides and supplied to the wind box 17 provided in the burner 1. Since the priority is given to reducing the amount of nitrogen oxides in this way, the control range of the exhaust gas circulation flow rate is planned to be significantly reduced compared to the conventional one.

In the boiler constructed as described above,
Conventionally, since the operation was performed at the standard load, seasoning proceeded in a manner close to the planned value, so there was no problem that the reheat steam temperature did not reach the planned value.

As shown in FIG. 3, the low-pressure turbine 10
Water pipe 1 connecting the condenser 18 and the economizer 13 connected to the
Reference numeral 9 indicates a low-pressure condensate pump 20, a desalting device 21, a low-pressure feed water heater 22, a deaerator 23, and a deaerator storage tank 2
4, a water supply pump 25, a high-pressure water supply heater 26, and a water supply flow meter 27 are sequentially provided.

[0011]

However, in recent years, due to the spread of nuclear power generation, the increase in operating rate, and the expansion of fluctuation range of electric power supply and demand, medium to large-sized oil-fired plants which have been conventionally constructed as base thermal power plants. Even in coal-fired thermal power plants, DSS operation has been started.
As a result, the temperature of the heat transfer tube frequently repeats high temperature and low temperature as the boiler starts and stops.Therefore, the difference between the elongation rate of the scale adhered and grown on the outer surface of the heat transfer tube and the elongation rate of the heat transfer tube is high. The scale peels off and falls off. Then, the heat transmission coefficient changes and the heat collection balance is lost, and, for example, the heat collection of the secondary heater 2 becomes excessive, while the reheaters 6, 7
However, there was a problem that the heat collection amount was reduced and the thermal efficiency was reduced. Further, when the operation of the nuclear power plant is unstable, it may return to the base thermal power operation, which makes it difficult to control the low temperature reheat steam from the high pressure turbine.

An object of the present invention is to provide a reheater outlet steam temperature adjusting device which can easily adjust the steam temperature discharged from the reheater.

[0013]

In order to achieve the above-mentioned object, a reheater outlet steam temperature control apparatus according to the present invention comprises a secondary superheater at the rear of a furnace of a boiler that burns fuel to generate steam. A reheater is arranged on the downstream side of the secondary superheater, and a flow channel for adjusting the steam temperature at the reheater outlet is provided on the downstream side of the reheater.

Further, the flow passageway may be detachably formed of a heat resistant steel plate.

Further, the flow passageway may be formed in a blade damper whose opening can be manually set.

[0016]

According to the above construction, by removing the flow channel weir provided in the gas flow channel in the downstream portion of the reheater, the passage area of the gas flow channel becomes wide, and the flow velocity of the gas passing through the outer surface of the heat transfer tube becomes slow. Become. On the contrary, the passage area is narrowed by attaching the flow channel, and the gas flow velocity is increased. Further, by using a damper structure in which the opening of the flow channel can be set, the gas flow velocity can be arbitrarily changed. As described above, the heat transmission coefficient can be changed by changing the gas flow rate outside the reheater tube, and the heat collection of the reheater which is not controlled by the heat collection of the secondary superheater can be formed. As a result, the reheat steam temperature can be adjusted.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the drawings. 1 and 2 show the configurations of the first and second embodiments of the present invention, respectively. In these figures, parts corresponding to those of the conventional example shown in FIG. 3 are denoted by the same reference numerals, and description thereof will be omitted as appropriate.

As shown in FIG. 1, the pipes of the reheaters 6 and 7 are arranged in the main gas flow passage 51 and the bypass flow passage 52 at a position of 25 to 50% in the height direction of the gas flow passage, with partition plates and casters. 53 is provided to configure the dividing partition. In addition, a cassette type baffle plate 54 having a height of 200 to 500 mm is provided in the bypass flow passage 52 as a flow passage which can be easily attached and detached by using a heat resistant steel plate. Then, under the same load condition, the flow velocity of the exhaust gas passing through the main gas flow path 51 is changed, the external heat conductivity of the reheater 7 is increased, and the heat collection amount in the reheater 7 is adjusted. In this case, the bypass channel 52 can be closed by the cassette type baffle plate 54.

According to the present embodiment, as a result of the DSS operation, the metal temperature of the heat transfer tube frequently repeats high temperature and low temperature, and as a result, the scale outside the tube drops off, the heat collection of the secondary superheater increases, and the reheater Of the reheater outlet steam temperature is lower than the reference value, the cassette type baffle plate 54 is attached to the bypass flow passage 52 to increase the heat transmission coefficient of the reheater.
Even if the heat collection of the secondary superheater does not change, the outlet steam temperature of the reheater can be increased.

In the second embodiment shown in FIG. 2, a cassette type partition plate 55 is provided in place of the partition plate and the caster 53 in the first embodiment, and is fixedly attached to the heat transfer tube by U bolts and nuts 56. .. Further, instead of the cassette type baffle plate 54, a pair of damper blades 57 are provided as a damper structure of a manual opening setting type, and the flow rate of the exhaust gas passing through the main gas passage 51 is changed depending on the opening of the damper blades 57. .. The damper blade 57 is attached to the damper partition plate 58.

According to this embodiment, the same effect as that of the first embodiment can be obtained.

[0022]

According to the present invention, since the gas flow velocity outside the reheater tube is variable, the reheated steam temperature does not reach the reference value due to operation change or fuel change during DSS operation or reference load operation. Can be prevented or minimized, and highly efficient operation of the plant becomes possible.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a first embodiment of the present invention.

FIG. 2 is a configuration diagram showing a second embodiment of the present invention.

FIG. 3 is a block diagram showing a configuration example of a boiler of a thermal power plant.

[Explanation of symbols]

 1 Boiler 2 Secondary superheater 6, 7 Reheater 54 Cassette type baffle plate (flow passage) 57 Damper blade (flow passage)

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tetsuji Nishi 6-9 Takaracho, Kure City, Hiroshima Prefecture Babcock Hitachi Ltd. Kure Factory

Claims (3)

[Claims] 1. A secondary superheater is provided at a rear portion of a furnace of a boiler that burns fuel to generate steam, and a reheater is provided downstream of the secondary superheater, and a downstream portion of the reheater is provided. A reheater outlet steam temperature adjusting device, characterized in that a flow channel is provided to adjust the steam temperature at the reheater outlet. 2. The reheater outlet steam temperature adjusting device according to claim 1, wherein the flow passage is made of a heat-resistant steel plate so as to be detachable. 3. The reheater outlet steam temperature adjusting device according to claim 1, wherein the flow passage is formed in a damper blade whose opening can be manually set.