JPS5818027Y2 - gas reheat device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a steam generator having a wet flapper, and more particularly to the reheating of gas leaving the wet flapper.

The gas exiting the wet flapper is saturated with water due to the scraping action and is usually mixed with some water.

This moisture corrodes downstream facilities and causes rainfall in the plant area.

Furthermore, the gases exiting the chimney produce relatively thick white smoke that is highly visible.

Therefore, to avoid such corrosion, precipitation, and increase in white smoke, it is common practice to reheat the gas immediately after scraping.

The primary heat source for exhaust gas reheating has been steam extracted from the turbine or hot water from the feed water cycle.

The use of extracted steam would dominate the total kilowatt output of the power plant, and the use of hot water from the feed water cycle would require the feed water cycle to be enlarged to accommodate this hot water supply. That will happen.

Since this feed water is heated by the exhaust steam, this also reduces the kilowatt output of the power plant.

According to the invention, high-pressure water is extracted from the lower drum of the steam generator and flowed into the tube side of the heat exchanger.

In this heat exchanger, heat is transferred to a low pressure fluid flowing on the shell side.

After leaving the heat exchanger, the high pressure water is returned to the steam generator at a location upstream of the boiler circulation pump.

A control valve is provided to control the flow of this high pressure water.

This high pressure water flow is controlled to minimize both its flow rate and return temperature.

Low pressure fluid circulates through a tubular reheat surface located downstream of each scrubber.

The reheater is arranged in parallel flow relationship with the low pressure fluid.

The flow through each reheater is adjusted according to the requirements of this particular scrubber.

The considerably lower flow of boiler water through the heat exchanger and the concomitant lower temperature of the return fluid act to reduce water losses through the furnace wall tubes. may increase losses.

Centrifugal pumps for circulating boiler water are constant volume devices within the scope of this specification, and the increased density of water due to cold return increases the mass flow of pumped water.

At high pressures this actually results in more water being pumped than passing through the heat exchanger.

The present invention will now be described in detail with reference to preferred embodiments illustrated in the accompanying drawings.

Steam generator 10 has a furnace 12 with furnace wall tubes 14 .

Feed water enters drum 16 where it is mixed with recycled saturated boiler water.

Saturated boiler water flows through a downcomer pipe 18 that includes a suction manifold 20, a circulating centrifugal pump 22, and a discharge manifold 24.

The circulation pump sucks boiler water from the manifold 20,
Discharge to manifold 24.

This water goes to the lower furnace wall header 26 and from there the furnace wall pipe 1
4 to the outlet header 28 and then to the steam drum 16.

Steam flows via line 30 to a superheater (not shown).

The fuel is burnt in the furnace 12 and the combustion gases are passed through the outlet duct 32.
and flows through a plurality of wet flappers 34, 36, etc.

This gas is scrubbed in the lower part of each scrubber and reheated in a tubular reheating surface 38,40.

The reheated gas passes through duct 42 to the chimney, from where it is exhausted to the atmosphere.

The steam generator operates at 364°C (688'F) and 396 kg/cm2 (2865 psig) gauge pressure.

After mixing with the feed water in drum 16, the recirculated water is at 362°C.
(684) and passes through downpipe 18.

Within the suction manifold 20, this flow is directed to the return line 44.
mix with water flow through.

This return pipe will be described later. The mixed water at a temperature of 361° C. (below 682° C.) passes through the circulation pump 22 and is recirculated through the steam generator furnace wall tube 14.

A portion of the flow goes from exhaust manifold 24 via supply line 46 to tube-end shell heat exchanger 48 .

High pressure water flows through the tube side of this heat exchanger and returns through return line 44.

Isolation valves 50 and 52 are provided for circuit isolation, while control valve 54 is a device that controls flow through the high pressure water loop.

A low pressure heat transfer loop is established on the shell side of heat exchanger 48.

Supply line 56 supplies low pressure fluid, e.g.
The scrubber gas is transported to multiple reheaters as shown in .

The low pressure fluid returns to heat exchanger 48 via return line 58 .

Circulation pump 60 operates to recirculate fluid at a suitable flow rate.

In this arrangement, heat is transferred from the boiler water to the low pressure fluid via the high pressure water circulating through the heat exchanger 48.

A controlled amount of this heat is then transferred to each of the tubular gas reheaters, and a controlled amount is used to reheat the gas to the desired level.

The low pressure fluid must be maintained at the lowest level necessary to reheat the gas to the desired degree.

The amount of high pressure fluid circulated is adjusted to control the temperature of the low pressure fluid.

Since the low pressure fluid is maintained at a reasonably low temperature, both the high pressure water flow rate and the high pressure water return temperature are minimized.

Temperature sensor 62 senses the temperature leaving scrubber 34 and sends a control signal to summing point 64.

This signal is between 66°C (150°F) and 93°C (200°F).
'F) is compared to the setpoint temperature 66, which is the desired gas temperature.

The error signal goes via control line 68 to controller 70 which actuates actuator 72 to modulate control valve 74.

This control valve 74 is connected to the supply pipe 56 and the return pipe 5.
The amount of low pressure fluid passing through the gas reheater 38 is controlled by varying the amount returned to the gas reheater 38.

Each of the scrubbers has a similar control loop operating in parallel to the others.

The temperature required in the low pressure loop is a function of the extent of the gas reheat surface, the required temperature of the reheated gas, and the amount of gas.

For the facility described above, the required temperature is 191°C (375°F)
, and therefore temperature sensor 76 issues a control signal via line 78 to summing point 80 where it is compared with setpoint 82 .

The error signal goes to controller 86 via control line 84.

This acts on actuator 88 to modulate control valve 54.

By modulating the control valve 54, the amount of high pressure water at 361'C (below 682) passing through the tube side of the heat exchanger 48 is changed.

This controls the temperature of the low pressure fluid.

The high pressure water returning through line 44 is at 249°C (480'F).
temperature.

This return high-pressure water is preferably distributed over the entire length of the section manifold 20 so as to obtain uniform mixing with the water passing through the upper portion of the downcomer pipe 18.

The circulation pump 22 is a centrifugal pump whose primary purpose is to circulate boiler water through the furnace wall tubes 14.

Within the range of interest in this embodiment, these pumps operate as constant volume pumps.

Total pump capacity 69650 l/m1n (18400g
pm).

If no heat was extracted for gas reheating, these pumps would generate 0.490 kg/m3 (0°03061
b/ft3) of water at 362°C (684'F).

This is 8.77 million kg (1.934 million kg) per hour.
1b).

168,600 kg (3,700,001 kg) of high-pressure water per hour required for heat exchange with a return temperature of 249°C (480'F)
The return in b) increases the temperature of the water to be pumped to 361℃ (6
82 below).

This is 0.479 kg/m3 (0,02991b/f
t3).

The flow rate of 69.000 l/min (18400gmp) is 8981280 kg/h (198 million
The flow is lb/h).

Therefore, 167,800 kg/hr (37
Even after subtracting 0000lb/h), the remaining 88130
00 kg/h (194.30000lb/h)
represents the actual increase in water over the amount that would be pumped without a heat exchanger.

Therefore, under these particular temperature and pressure conditions, not only will there be no harmful effects on the water tube wall, but the practical benefit of being able to circulate the water tube wall with the same pump can be obtained.

It can be seen that this phenomenon, where the use of a heat exchanger can actually increase the wall circulation rate, is more likely to occur at high temperatures and pressures where the specific volume of water changes more rapidly with changes in enthalpy than with changes in temperature.

However, even in situations where the furnace wall flow does not increase, by using the lowest allowable temperature in the low pressure loop, and by concomitantly minimizing the flow in the high pressure loop and minimizing the return temperature. , the above-mentioned reduction can be minimized.

Similar results can be obtained without a circulation pump, as long as the return water is not returned to a higher location.

This is because the density of the water in the downcomer increases and thus the boiler water circulation increases.

However, under these circumstances, if a circulation pump is not used in the steam generator, a separate pump would be required in the high pressure recirculation loop.

[Brief explanation of drawings]

The accompanying drawing is a diagrammatic representation of a preferred embodiment of the present invention. 10... Steam generator, 12... Furnace, 1
4... Furnace wall, 16... Drum, 18.
... Downpipe, 20 ... Suction manifold, 22 ... Circulation centrifugal pump, 24 ...
... Discharge manifold, 26 ... Lower furnace wall header, 28 ... Outlet header, 30 ... Pipe line, 32 ... Outlet pipe), 34 .36...
... Wet flapper, 38.40 ... Tubular reheating surface, 42 ... ... Duct, 44 ... Return pipe line, 46 ... ... Supply pipe line , 48...
Tube end shell heat exchanger, 50.52...
...Shutoff valve, 54...Control valve, 56...
・Supply pipe line, 58...Return pipe line, 60...
... Circulation pump, 62 ... Temperature sensor, 64
...Additional point, 66...Set point temperature, 6
8... Control line, 70... Controller, 72... Actuator, 74...
・Control valve, 76...Temperature sensor, 78...
...Railway, 80...Additional points, 82...
Set point, 84... Control line.

Claims (1)

[Scope of utility model registration request] a steam generator comprising pipes lining the furnace walls and carrying water and a downcomer arrangement arranged to recirculate water from a position downstream of these pipes to a position upstream of these pipes; A gas reheating device having a wetscloth flapper for receiving exhaust gas from a steam generator and discharging the exhaust gas to the atmosphere, and a tubular gas reheating surface disposed in the exhaust gas stream from each wetscloth flapper, a heat exchanger, a device for conveying a low pressure fluid from the heat exchanger to and from each of the gas reheat surfaces, and a device for conveying the low pressure fluid into the heat exchanger and further to the gas reheat surfaces; and a device for circulating high pressure water from the downcomer system through the heat exchanger in heat exchange relationship with the low pressure fluid and returning the high pressure water to the downcomer system. Characteristic gas reheating equipment.