JPS6243048B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a waste heat recovery power generation plant, and particularly provides a waste heat recovery power generation plant that takes into account fluctuations in waste gas temperature and has good waste heat recovery power generation efficiency.

BACKGROUND OF THE INVENTION Since it is predicted that oil resources will soon be depleted, various methods have been attempted to utilize energy effectively. For example, in mining and industrial production systems (hereinafter referred to as production systems), efforts are being made to save energy by preheating raw materials using the residual heat or waste heat of products, but there are also energy savings that cannot be used in production systems. A device has been proposed for recovering electrical power from waste heat at a level. 1st
The figure shows the system of a conventional waste heat recovery power generation plant. In FIG. 1, 1 is an evaporator, 2 is a preheater, 4 is a generator driven by a turbine generator 3, 5 is a condenser, and 6 is a condenser 5
This is a pump that sends water from the air to the preheater 2. Evaporator 1 is
It consists of an upper drum 7, a heating tube 8, a lower drum 9 and a downcomer 10. Water-steam can be used as the working medium in such waste heat recovery power generation plants if the waste gas temperature is high enough, but usually water-steam is used as the working medium in the production system, which is the waste gas source. Since the temperature has dropped to 400°C, low boiling point media (hereinafter referred to as media) such as trichlorotrifluoroethane and trichlorotrifluoromethane are used from the viewpoint of waste heat recovery power generation efficiency. The medium is preheated in the preheater 2 to a temperature close to the saturation temperature of the supply pressure, and is further supplied to the upper drum 7 of the evaporator 1 through the liquid supply pipe 11. In the evaporator 1, the medium is heated by the waste gas in the heating tube 8, and a part of the medium is vaporized. Along with this, bubbles of the medium are generated in the heating tube 8, and due to the density difference with the medium in the downcomer tube 10, the system consisting of the upper drum 7, downcomer tube 10, lower drum 9 and heating tube 8 Circulating flow occurs. The generated medium steam is separated in the upper drum 7, supplied to the turbine 3 through the main steam pipe 13 to recover power, and returns to the preheater 2 from the condenser 5 via the pump 6, forming a closed cycle. Note that 16 and 17 indicate waste gas cylinders.

Such conventional waste heat recovery plants have the disadvantage that the efficiency of waste heat recovery and power generation is low when the temperature of the waste gas fluctuates. In other words, when designing a waste heat recovery power generation plant, the heat source temperature is set to approximately the average temperature after comparing the waste gas conditions of the production system, but in actual equipment, the waste gas temperature constantly fluctuates depending on the production status of the production system. do. In a conventional constant load operation plant, when the exhaust gas temperature becomes higher than the design temperature, a part of the exhaust gas is discharged to the outside by adjusting the damper 19 of the exhaust gas supply cylinder 15 and the bypass damper 18 of the bypass discharge cylinder 20. By reducing the amount of waste gas supplied to the evaporator 1, the amount of evaporation of the medium is adjusted, thereby suppressing the power generation output to the rated output. Also, conventionally,
When the exhaust gas temperature fluctuates, the evaporation amount of the evaporator 1 is increased without adjusting the exhaust gas supply amount, and the turbine 3
bypass steam pipe 14
It may also be discharged to a condenser 5 for cooling.

Furthermore, when the exhaust gas temperature falls below the design temperature, the amount of evaporation of the medium in the evaporator 1 decreases, but the temperature difference between the exhaust gas and the medium in the preheater 2 increases, and the temperature inside the preheater 2 increases. The medium will come to a boil. The boiling phenomenon of the medium in the preheater must be avoided because it can damage the heat exchanger tubes and have a large effect on the stable operation of the plant.
In conventional plants, as shown in Fig. 1, the medium discharge pipe of the preheater 2 is branched to provide a bypass liquid pipe 12, and when the waste gas temperature falls below the design temperature, the amount of medium supplied to the preheater 2 is reduced. The increased amount is transferred to the condenser 5 through the bypass liquid pipe 12 to prevent the medium from boiling.
It is cooled by releasing it to the

The amount of bypass waste gas released, bypass steam released, or bypass liquid released increases as the difference between the waste gas temperature and the design temperature increases. This means that while the heat energy is recovered, it is disposed of in the condenser without being turned into power.

We calculated the operating status of a conventional plant under such fluctuations in waste gas temperature. The calculation conditions are: design waste gas temperature 250℃, waste gas amount 480000Nm ³ /k, using the above-mentioned trichlorotrifluoroethane as the heat recovery medium, operating pressure 14Kg/cm ² , evaporator pinch point 24℃, preheater outlet. Medium subcool temperature of 10
℃. A waste heat recovery power generation plant was designed under these conditions, and the heat balance when the waste gas temperature fluctuated in a sinusoidal manner within a range of ±30°C was determined by setting the preheater outlet medium subcool temperature to 10°C or higher. Second
The figure shows the trial calculation results. Here, the cycle time of waste gas was calculated as 1 hour. When the waste gas temperature is the rated design temperature of 250°C, a power generation output of approximately 2810 kW is obtained, and the bypass steam release flow rate or the equivalent waste gas bypass release flow rate and bypass liquid release flow rate are zero. When the waste gas temperature exceeds the design temperature of 250°C, the amount of evaporation in the evaporator 1 increases, but the increased amount is released into the condenser 5 through the bypass steam pipe 14 (bypass steam flow rate), or the amount of waste gas equivalent to the amount is reduced. External discharge is achieved by adjusting the damper 19 and the bypass damper 18. This controls the main steam flow rate and keeps the power generation output constant. On the other hand, it is natural that the amount of medium evaporation and power generation output decrease when the exhaust gas temperature decreases;
Along with this, the bypass discharge liquid flows out, and the amount becomes larger as the temperature becomes lower.

In this way, in conventional waste heat recovery power generation plants,
When the temperature of waste gas generated varies depending on the production status of the production system, some of the high-temperature waste gas can be disposed of, or the heat energy can be recovered and radiated to a cooling source without converting it into electric power. There is.

An object of the present invention is to eliminate the above-mentioned conventional drawbacks, and to provide a waste heat recovery power generation plant that utilizes effective energy when the temperature of waste gas fluctuates to increase power generation output and has good waste heat recovery power generation efficiency. be.

The present invention installs a heat storage device that heats and stores heat using a part of the waste gas, and heats and vaporizes preheater bypass liquid with the heat storage device to increase power generation output.

An embodiment of the present invention will be described with reference to FIG. In FIG. 3, components that are the same as the conventional ones are indicated by the same numbers as in FIG.
2. It is a heat storage device loaded with heat transfer tubes 23 through which a medium passes. The heat storage device 21 is connected to a bypass discharge shell 20 for supplying bypass discharged waste gas, a bypass liquid pipe 12 for guiding preheater bypass discharged liquid, and further for supplying generated steam to the main steam pipe 13 from the evaporator 1. A steam pipe 25 is installed. The heat storage material 22 includes materials that store heat using sensible heat such as concrete, coal stone, and non-flammable oil, and materials such as KNO ₃ -NaNO ₂ -NaNO ₃ (53-
40-7w%, mp142℃, latent heat of fusion 19.4kcal/Kg),
FeCl ₃ - NaCl (76.5-23.5w%, mp158℃, latent heat of fusion 37.7kcal/Kg), KOH-NaOH (59-41w
%, mp 170°C, latent heat of fusion 55.1 kcal/Kg), etc., that utilize the latent heat of fusion associated with solid-liquid phase change. In order to heat the medium, which is the object to be heated, to a constant temperature that drives the turbine, it is preferable to use a heat storage material that uses latent heat that has a melting point close to the main steam temperature. As in this case, or when the heat storage material is a liquid such as non-flammable oil, the heat storage material 2
2 may be filled in a small volume or placed in a blood vessel. Further, although the heat storage device 21 in FIG. 3 has a structure in which the heat storage material 22 is built-in, the heat storage material may be placed separately and circulated through a heat exchanger. Note that 26 indicates a waste gas cylinder.

In this system, when the exhaust gas temperature is approximately the same as the rated design temperature, the operation method is the same as that of the conventional plant. The functions and effects of the present invention appear when the temperature of the exhaust gas fluctuates due to changes in the production status of the production system that is the heat source. That is, when the exhaust gas temperature rises above the rated design temperature, the amount of exhaust gas supplied to the evaporator 1 is reduced by adjusting the opening degrees of the damper 19 and the bypass damper 18.
The amount of evaporation is suppressed to the amount of steam required for rated operation. The excess amount of waste gas is transferred from the bypass discharge cylinder 20 to the heat storage device 21.
heats the heat storage material 22 and stores heat. Next, when the waste gas temperature falls below the design temperature, the amount of medium supplied is increased to prevent the medium from boiling in the preheater 2, and the increased amount is guided to the heat storage device 21 through the bypass liquid pipe 12, and is stored through the heat transfer pipe 23. Material 22
The steam is heated and vaporized, and the generated steam is supplied from the steam pipe 25 to the main steam pipe 13 and the turbine 3 to obtain electric power.

The effects of the present invention were estimated under the same conditions as the conventional example. The trial calculation results are shown in Figure 4. In this calculation, the heat storage material 22 of the heat storage device 21 is an example of a heat storage material having a melting point close to the boiling point of approximately 156°C at a supply pressure of 14 Kg/cm ² of the refrigerant trichlorotrifluoroethane.
Estimated using FeCl ₃ -NaCl (mp 158℃).
In Fig. 4, the evaporator generated main steam flow rate is the main steam flow rate generated in the evaporator 1 and supplied to the turbine 3, and when the waste gas temperature is higher than the rated design temperature of 250°C, part of the waste gas is released by bypass. Although it is a constant amount, it decreases rapidly below the design temperature. The effective heat storage amount is the usable heat storage amount stored in the heat storage device 21, that is, the heat amount equivalent to the preheater bypass medium liquid temperature or higher, and the exhaust gas temperature is the rated design temperature.
It is stored by bypass discharged waste gas when the temperature is above 250℃. The required heat storage capacity of the heat storage device 21, that is, the required amount of the heat storage material 22, needs to be the amount that can store the maximum effective heat storage amount, and in the case of this trial calculation example, the maximum effective heat storage amount is approximately 7 × 10 ⁵ kcal. From about 18500Kg
FeCl ₃ - requires NaCl. Further, in FIG. 4, the regenerator heating main steam flow rate of the bypass liquid is the medium steam flow rate when the bypass liquid in the preheater 2 is heated and evaporated by the heat storage device 21 when the exhaust gas temperature drops to the design temperature of 250°C or less. In the present invention, this steam increases the power generation output. At this time, the effective heat storage amount of the heat storage device gradually decreases because heat is radiated to the medium. Furthermore, as the exhaust gas temperature decreases, the amount of preheater bypass liquid increases, so the amount of generated steam increases. Note that the effective amount of heat storage immediately after the plant starts operation is zero because the temperature of the heat storage material 22 is room temperature, but under continuous operation, the minimum usable heat storage material temperature (i.e., preheating medium temperature) is set as the lower limit as shown in Figure 4. It can be used continuously as shown.

As shown in FIG. 4, it can be seen that the power generation output in this example is greater than the power generation output (dotted line) of the conventional plant. The amount of power generated per cycle of waste gas temperature fluctuation (1 hour in this trial calculation) is approximately 2,690kw/h in the present invention, compared to approximately 2,460kw/h in the conventional example.
It increases by about 9.3% from h. The rate of increase varies depending on the fluctuation range of the exhaust gas temperature, and the calculation results are summarized in FIG. 5. When the exhaust gas temperature fluctuates by ±30°C, ±40°C, and ±50°C with respect to the rated design temperature of 250°C, the temperature decreases by approximately 9.3% and 13% compared to conventional methods, respectively.
%, an increase in power generation of 17.5% is expected.

Although representative embodiments of the invention have been described above, other implementations are possible within the scope of the invention. In other words, in the above explanation, we have shown the operation method when the waste gas temperature of a constant load operation plant differs from the rated design temperature, but in a load following operation plant, the same operation method can also be performed by measuring the medium pressure of the evaporator. can be done and have the same effect. When the load on the turbine generator is less than the heat capacity of the waste gas (that is, the amount of evaporation in the evaporator), the medium working pressure of the evaporator tends to increase, and in order to prevent this pressure from increasing, some of the waste gas is is guided to a heat storage device to store heat. On the other hand, when the load is higher, the operating pressure of the evaporator tends to decrease, so in order to prevent the pressure from decreasing, the amount of evaporation in the evaporator is suppressed and a portion of the preheating medium liquid is guided to the heat storage device. It is possible to increase the power generation output by heating and evaporating the generated steam and supplying it to a turbine generator.

In the examples of the present invention, trichlorotrifluoroethane was used as a medium, and trial calculation conditions were determined and shown. However, other low boiling media and operating conditions may be used depending on the temperature level of the waste gas. Furthermore, in the trial calculation of the effects of the present invention shown in FIG. 4, the exhaust gas temperature fluctuation cycle was set to 1 hour, but the effects of the invention are the same even if the cycle is longer or shorter.
In this case, it is necessary to set the required heat storage capacity of the heat storage device to an amount commensurate with its cycle time and temperature fluctuation range. In addition, in the embodiment of the present invention, the heat storage material
Although FeCl ₃ -NaCl was used in the description, it goes without saying that other heat storage materials and heat storage methods may be used depending on the exhaust gas temperature and medium evaporation temperature.

As described above, according to the present invention, it is possible to increase the power generation output by using effective energy when the waste gas temperature fluctuates due to changes in the production status of the production system.
A waste heat recovery power generation plant with good waste heat recovery power generation efficiency can be provided.

[Brief explanation of the drawing]

Figure 1 is a system diagram of a conventional waste heat recovery power generation plant, Figure 2 is a diagram showing the estimated power generation output when the waste gas temperature fluctuates in the conventional plant, and Figure 3
Figure 4 is a system diagram of a waste heat recovery power generation plant showing an embodiment of the present invention, Figure 4 is a line diagram showing the results of trial calculations of power generation output when the temperature of waste gas fluctuates in the plant implementing the present invention, and Figure 5 is FIG. 3 is a diagram showing the effects of the present invention in comparison with a conventional example. 1... Evaporator, 2... Preheater, 3... Turbine, 4... Generator, 5... Condenser, 6... Pump, 12... Bypass liquid pipe, 13... Main steam pipe,
15... Waste gas supply cylinder, 20... Bypass discharge cylinder, 21... Heat storage device, 22... Heat storage material, 25...
...steam pipe.

Claims (1)

[Claims] 1. A turbine that has a preheater that heats a low boiling point medium using waste gas and an evaporator that evaporates the heated low boiling point medium, and that operates with the steam of the evaporated low boiling point medium, and a turbine that is driven by this turbine. In a waste heat recovery power generation plant, the plant has a generator that is used to generate electricity, a condenser that condenses and liquefies the steam worked by the turbine, and a pump that sends the low-boiling medium that has been liquefied in the condenser to the preheater. A heat storage device stores the heat of the waste gas using a heat storage material that utilizes the latent heat of fusion caused by the solid-liquid phase change of the substance or the sensible heat caused by the temperature difference, and the waste gas is heated by the preheater. A part of the low boiling point medium is supplied to the heat storage device, the low boiling point medium supplied to the heat storage device is evaporated by the heat storage material, and a pipe line is provided to supply the evaporated low boiling point medium to the turbine. Waste heat recovery power plant.