FI72193B - FOERFARANDE FOER REGLERING AV AONGGENERERINGSKAPACITETEN HOS EN AVGASAONGPANNEANLAEGGNING SAMT FOER GENOMFOERANDE AV DETTAFOERFARANDE AVSEDD AVGASAONGPANNEANLAEGGNING - Google Patents

Description

1 72193

TECHNICAL FIELD steam boiler plants for converter installations, power stations, etc. in factories. The invention relates in particular to methods for controlling the steam output of waste boilers and to waste boiler plants implementing such a method.

A method is known for controlling the steam output of a waste boiler plant comprising more than one pressure circulating type waste heat boiler, each of which varies the gas flow rate (cf. e.g., Gerlovin LI & Slutsker AS, "Sudovye utilizatsionnye i kombinirovanrye kot 34-35, 90-91, Khrapchenkov AS, "Sudovye vspomogatelnve i utilizatsionnye parogeneratory", Sudostroenie Publishers, 197y, page 220, Figure 1.19}.

A waste heat boiler plant implementing this known method is also known, which comprises a plurality of waste heat boilers which are connected to a common steam separator via a pressure circuit provided by a pump or pumps. The plant is equipped with flue dampers that act as means to regulate the flow of hot gas through each boiler. They are programmed to operate in a specific order, either sequentially or in parallel.

In practice, however, the known control method causes a reduction in steam output compared to the output under certain conditions when different amounts of heat are introduced into the boilers, regardless of the 2 72193 dampers set to be fully open. The explanation for this is that waste boilers heated with gases of different temperatures are fed with water of the same temperature. This degrades the efficiency of the heat absorbing surfaces or in other words reduces the overall steam output of the waste boilers.

Another feature is that when using this method to control the steam output of a waste boiler plant, the thermal conditions of each boiler are not monitored. This can lead to the temperature of the gases coming with the heat-absorbing surfaces of the waste boiler falling to a value which is too low in relation to the risk of corrosion at such a temperature. Thus, for example, a boiler using the exhaust gas of a part-load machine is heated by gases having a lower temperature. An increase in the vapor pressure in the steam separator can cause the controller to close, as determined by the steam output control method, the damper located precisely on this machine before the waste heat boiler. This results in a further decrease in the temperature of the gases downstream of the boiler (already too low due to the operation of the gas generating machine at part load) to an unfavorable level.

With regard to low temperature corrosion, the minimum permissible temperature of the circulating water is 135-150 ° C. This temperature is either specified by the boiler manufacturer or is determined during operation by the "acid dew point", which can be calculated if the sulfur content of the fuel and the excess air factor are known. In these cases, when the circulating water temperature at the inlet of the preheater boiler exceeds the minimum value allowed for low temperature heat absorbing surface corrosion, not all the heat supplied by the exhaust gases will be used in the boiler. The resulting reduction in the difference between the temperature of the hot gases and the temperature of the heat-absorbing surface impairs the economy of the plant.

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Furthermore, a method is known for controlling the steam output of a boiler plant comprising a pressure circulating waste heat boiler and an oil-fired boiler forming a single water circuit in which the circulating water fed to the boiler is cooled by feed water so that the circulating water temperature is not lower than Temperature control is achieved by dividing the feed water between the water space of the oil-fired boiler and the feed tank of the associated waste heat boiler (USSR Inventor's Certificate No. 817374, Int. Cl.3 F 22 B 1/00, F 22 D 5/00, 1982).

In practice, this method is mainly limited to the control of steam generating equipment comprising one waste boiler and one oil-fired boiler. It cannot be effectively used to control steam generating equipment comprising a plurality of pressure circulating waste heat boilers.

The explanation is that according to a known method, applied to the co-operation of a waste boiler and an oil boiler, the circulating water supplied to a waste boiler heated by gases having a lower temperature than the oil boiler can be cooled to the minimum permissible temperature with feed water. However, this cannot be guaranteed in a plant consisting of several waste boilers. In addition, in this known method of controlling steam production, the boilers are fed with circulating water having the same temperature in each boiler, regardless of the heating conditions prevailing in the boiler.

A waste heat steam boiler plant is also known in the art, comprising two boilers connected to a common steam separator by means of a pump so that they can be started either sequentially or in parallel. The inlet of each boiler is equipped with means for measuring the temperatures of gases and circulating water. When the main engines start running at 4,724,193 part loads (i.e., the amount of heat input to each boiler decreases), the steam output controller will cause the boilers to operate more sequentially than in parallel, so that the first boiler in the circulating water flow direction will operate like a preheater and the second boiler.

This boiler plant and the method for controlling its steam output are described in: Ivanov V.D. & Smirnov Ju.A., "Expluatatsia kotelnykh ustanovok diselnykh sudov", Transport Publishers, 1971, page 146, Fig. 76.

This plant is only useful in cases where the gas temperature before the first waste boiler in the circulating water flow direction is not higher than the temperature before the second boiler, i.e. when the first boiler operates like a preheater and the second boiler under evaporative conditions. It should also be noted that the steam separator is supplied with feed water in an amount corresponding to the total steam output of the boilers without taking into account the prevailing conditions in which each of the boilers operates. This can lead to a situation where the circulating water temperature falls below the minimum permissible value, regardless of whether the boilers are connected in parallel or in series. Such conditions would be likely to accelerate corrosion at low temperatures, which in turn would degrade the reliability of the boiler plant.

Thus, all known methods for controlling the steam output of waste boilers in steam boiler plants carrying out these methods, which comprise more than one waste boiler, have the necessary reduction in steam output and insufficient reliability under certain conditions, for example when the heat generating machines operate in partial envelopes. The explanation is that the temperature of the circulating water discharged to each boiler in the plant is not affected by the gas temperature upstream of the boiler 5 72193. In order to achieve the maximum value of steam production and good operational reliability, it is necessary to maintain the operating conditions of boilers heated with lower temperature gases close to the preheater mode and the operating conditions of boilers heated with higher temperature gases close to the evaporator mode.

The main object of the present invention is to provide a method for controlling the steam output of a waste heat boiler plant by providing a chain of events and a plant structure that allows waste .

On the other hand, this object is achieved by and the circulating water of the boilers is cooled successively by the feed water starting from the boiler in front of which the gas temperature is lowest, and the circulating water of each subsequent boiler is cooled by the feed water when the water supplied to the previous boiler is cooled to the minimum permissible temperature.

The object of the invention is achieved, on the other hand, in a waste boiler plant comprising at least two pressure circulating type at the inlet points of the boilers, the plant also comprising, according to the invention, heat exchangers, control valves and feed valves. for sharing between the heat exchangers and a central control unit for comparing the gas temperatures and producing signals controlling the operation of the control valves, the heat-absorbing surface of each heat exchanger being located in the supply water line and the steam separator. between, the heat transfer surface of each heat exchanger being located between the circulating water pump and the heat absorbing surface of each boiler and the outputs of the temperature sensors being connected to the inputs of a central control unit whose outputs are connected to control valves.

The invention provides for an increase in the steam output of waste boilers by supplying circulating water with a minimum permissible temperature to those boilers which are heated with gases having the lowest temperature. In other words, the invention makes the boilers operate essentially like a preheater. On the other hand, boilers that receive higher temperature gases are fed with circulating water at a temperature close to the boiling point, so that these boilers will operate approximately like an evaporator. The invention provides an optimum distribution of heat output between the boilers, using the heat of the hotter gases mainly to generate steam and the heat of the cooler gases to preheat the water to the boiling point, thus ensuring maximum steam production under all operating conditions. This has become possible in practice because the parts of the waste-boiler plant are connected to each other according to the invention in such a way that it is possible to control the temperature of the water fed to the boilers depending on the relationship between the gas temperatures in front of the boilers.

The method according to the invention for controlling the steam output of a waste boiler plant comprises measuring the circulating water and gas temperatures before each boiler, comparing the 11,772,193 gas temperature values thus obtained and cooling the circulating water fed to the boilers with feed water from the boiler to the boiler. If the temperature of the circulating water supplied to a particular boiler has already been reduced to the minimum permissible value for corrosion at low temperatures, this temperature must be maintained by a continuous supply of supply water. The cooling of the circulating water in the other boilers must be continued with the remaining feed water, starting with the boiler with the lowest gas temperature. Such control provides an optimal distribution of heat supply between the waste boilers of the plant, regardless of the heating conditions.

The waste heat steam boiler plant shown in the accompanying drawing comprises three boilers 1, 2, 3, each of which has a heat absorbing surface together with a pressure circuit inlet pipes 4, 5, 6, its outlet pipes 7, 8, 9 and a steam separator 10. The steam separator 10 communicates with the supply water line 11 via heat-absorbing surfaces 12, 13, 14 of heat exchangers 15, 16, 17, which surfaces are connected in parallel. Control valves 18, 19, 20 are located in the inlet lines of the heat exchangers 15, 16, 17. Each of the waste heat boilers 1, 2, 3 is connected to a corresponding pressurized water circulation pipe 4, 5, 6 via the heat transfer surfaces of the heat exchangers 15, 16, 17. The function of the pump 24 is to provide water circulation in the inlet pipes 4, 5, 6. The plant is further provided with a feed water pump 25 controlled by a supply water flow controller 26 connected to a water level sensor 27 in the steam separator 10. The steam pipe 28 leading to the steam drive The control valves 18, 19, 20 are connected to a central control unit 29, which in turn is connected to the circulating water temperature sensors 30, 31, 32 and the gas temperature sensors 33, 34, 35 before the waste heat boilers 1, 2, 3. A bypass line 36 comprising a shut-off valve 37 is connected in parallel with water circulating pipes 4, 5, 6.

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The plant operates as follows: Inside the steam separator 10, some water is pumped using the pump 24 through the heat transfer surfaces 21, 22, 23 of the heat exchangers 15, 16, 17 to the heat absorbing surfaces of the waste heat boilers 1, 2, 3. In boilers, the water heats up, some of it evaporates, due to the heat transferred from the exhaust gases to the heat-absorbing surfaces. The mixture of water and steam enters the steam separator 10, where the steam is released from the water. The amount of feed water fed to the waste heat boiler plant is regulated by the supply controller 26 according to the signals produced by the water level sensor 27 in the steam separator 10. Prior to the waste heat boilers 1, 2, 3 in operation, the prevailing gas temperature is monitored by means of temperature sensors 33, 34, 35 connected to the control unit 29. The control signal produced by the control unit 29, after the unit has compared the gas temperatures prevailing before the boilers 1, 2, 3, is fed to control valves 18, 19, 20 which distribute the supply water flow between the heat exchangers 15, 16, 17 from the boiler currently heated by low temperature gases. The circulating water temperature sensors 30, 31, 32 are also connected to the central control unit 29.

The computer program used for monitoring and controlling the power generating devices is in this case a logic program suitable for the control unit 29.

One feature of the operation of the above-mentioned waste boiler plant is that the cooling feed water is fed to the heat exchanger of the waste boiler operating at the minimum value of the gas temperature until the circulating water temperature in this boiler is at the minimum permissible level. No feed water is allowed into the heat exchangers of the other waste boilers until the circulating water temperature in the previous boiler has reached the permissible minimum level.

Valve 37 is normally closed and serves to allow water to enter the steam separator 10 during plant start-up.

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The following is a discussion of how the plant operates under varying temperature conditions. Assume that the control unit 29, after comparing the gas temperatures prevailing by the temperature sensors 33, 34, 35 before the waste heat boilers 1, 2, 3, indicates that the temperatures increase in the boiler order 1-2-3. This means that the lowest temperature prevails before boiler 1 and the highest before boiler 3. Corresponding to the plant load, the feed water is introduced into the steam separator 10 by means of the feed regulator 26. In this case, the amount of feed water passing through the control valve 18 must keep the recirculated water temperature measured by the sensor 30 at its minimum allowable temperature due to low temperature corrosion and the amount of water passing through the control valve 19 must replenish the water in the steam separator 10. This will cause the temperature , which should be maintained to prevent low temperature corrosion. The valve 20 is closed and the temperature monitored by the sensor 32 approaches the boiling point, since no water cooling takes place in the heat exchanger 17 using the feed water.

If the temperature before boiler 1 rises due to changed operating conditions, exceeding the temperature before boiler 3, the order of temperature rise of the boilers should be 2-3-1 and not 1-2-3. The valve 19 triggered by the signal produced by the control unit 29 opens, allowing the feed water to flow to the heat exchanger 16 and from it to the steam separator lo in an amount necessary to maintain the temperature monitored by the sensor 31 (i.e. before boiler 2) at its minimum value for low temperature corrosion. Immediately after reaching this value, the control valve 20 is opened. If the water level in the steam separator 10 is currently at a suitable height and the water temperature T: 10 721 93 monitored by the sensor 32 is above the minimum permissible value, no supply water needs to be discharged through the control valve 18. Otherwise, the feed water is fed to the heat exchanger 15 via the control valve 18 as soon as the water temperature monitored by the turmer 32 has reached its minimum value. The water temperatures monitored by the recognized 31 and 32 are also kept at this minimum value.

The above method of interconnecting the different parts of a waste heat boiler plant makes the plant suitable for the described steam production control method. The fact that the circulating water fed to the waste boilers is at all temperatures under the operating conditions which, according to the method described, are never below the minimum permissible value for corrosion at low temperatures ensures the reliable operation of the entire waste heat boiler plant. In addition, the fact that the heat from the highest temperature gases is mainly used for steam generation, while the heat from the low temperature gases is mainly used to heat the water to boiling point, ensures an increase in steam production in the waste boiler plant under conditions different from those for which the plant is designed, e.g. in the event of intermittent variations in the heat entering the boilers.

The increase in steam output of a waste heat steam boiler plant that can be achieved by using the optimal distribution of heat input between the boilers under the prevailing operating conditions is 3-5%. The time between boiler renovations will be extended by 15-20%.

Claims (2)

A method for controlling the meadow generation capacity of an exhaust gas boiler system, comprising at least two forced circulation exhaust gas boilers, by measuring the temperature of circulating water at each exhaust gas boiler (1, 2, 3) inlet and constant pouring this temperature at a value which is not lower than the minimum permissible temperature, characterized by measuring the gas temperature above the exhaust gas boilers in operation (1, 2, 3) and comparing the obtained gas temperature values with each other and gradually cooling the circulation water in the exhaust gas boilers (1, 2, 3). ) by means of feed water initially, each thread, from the exhaust gas boiler with the minimum gas temperature, the circulating water of each subsequent exhaust steam boiler being cooled only by feed water, if the water to be fed into the previous exhaust steam boiler is cooled to the minimum permissible temperature. 2. Exhaust gas boiler system for carrying out the method according to claim 1, which comprises at least two forced gas exhaust gas boilers (1, 2), whose heating surfaces by supply and drain circulation pipelines (4, 5 and 7, 8) are connected to closed circuits. with a meadow separator (10), and one connected with the meadow separator (10), with a supply regulator (26) provided with piping (11) for feed water and partly means for measuring the gas and circulation water temperature at the exhaust bed boilers (1, 2). inlet, characterized in that it is provided with heat exchangers (15, 16, 17), control valves (18, 19, 20) intended for distribution of feed water between the heat exchangers (15, 16 and 17, respectively), and a central control device (29) , which are intended to compare the gas temperature values with each other and to form signals for controlling the control valves (18, 19, 20), each duct system (12, 13 and 14) of each heat exchanger ( is provided between the feed water pipe (11) and the mud separator (10), while the heating duct system (21, 22 and 23, respectively) of each heat exchanger (15, 16, 17) is arranged between a circulation pump II