JPS5937438B2 - Method of recovering heat from exhaust gas - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a heat medium used for heat recovery in an exhaust heat recovery system installed in an exhaust gas treatment discharge passage of an incinerator, etc., and the boiling point of the heat medium is lower than the temperature of the gas flowing into the heat exchanger. The present invention relates to a method of recovering heat from exhaust gas using a high heat medium.

Conventionally, exhaust gas discharged from an incinerator or the like is subjected to dry gas treatment and then supplied to a waste heat boiler for heat recovery.

Then, the exhaust gas from the waste heat boiler is discharged into the atmosphere from the chimney after removing dust from the exhaust gas in an electrostatic precipitator.

The exhaust gas temperature at the exit of the electrostatic precipitator is generally around 300°C in conventional incineration plants.

Therefore, the exhaust gas at the outlet of the electrostatic precipitator still retains a large amount of heat from the viewpoint of energy conservation.

There are various problems when configuring a heat recovery system downstream of the electrostatic precipitator in order to recover such heat.

First, low-temperature corrosion that occurs in heat exchangers became a problem, and secondly,
Due to its nature, the amount of heat held by the exhaust gas from an incinerator, etc. is generally unrelated to load fluctuations in the heat recovery system, as described above. If you try to control it, for example, when water is used as a heat medium, when the load on the heat recovery system is almost gone, the pressure in the heat recovery system will increase due to water evaporation, making it impossible to freely control the amount of heat exchanged. Furthermore, when water is used as a heat medium, the range of utilization of the recovered heat is narrow.

The purpose of the present invention is to prevent low-temperature corrosion of the heat exchanger and to recover the heat by supplying a heat medium with a boiling point higher than the exhaust gas temperature supplied to the heat exchanger of the heat recovery system to the heat exchanger. An object of the present invention is to provide a method for recovering heat from exhaust gas, which can freely control the amount of heat exchange by controlling the flow rate of the exhaust gas, and achieve multipurpose use of the recovered heat.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a block diagram of an example of an apparatus implementing the method of the present invention.

An electrostatic precipitator 2c and a chimney 2d of an exhaust gas processing passage 2 that processes exhaust gas from an incinerator 1, etc., and is composed of a dry gas treatment means 2a, a waste heat boiler 2b, an electrostatic precipitator 2c, and a chimney 2d.
A heat exchanger 3 is interposed between the two.

The heat medium outlet of the heat exchanger 3 is connected to a heat load device 5 via an auxiliary heat exchanger such as a steam heat exchanger 4 provided as necessary.
is connected to.

The outlet of the heat load device 5 is connected to the inlet of the heat exchanger 3 to form a heat recovery circulation system 6.

The steam heat exchanger 4 is a means for receiving steam from the waste heat boiler 2b to compensate for the shortage in the heating amount of the heat medium in the heat exchanger 3.

4a' which imparts thermal energy to the heat medium and is sent to a condensate tank (not shown) for condensation;

The heat medium has a boiling point at the exhaust gas temperature at which it flows into the exhaust gas inlet of the heat exchanger (the exhaust gas temperature at the outlet of the electrostatic precipitator is usually around 300°C).

) higher temperature e.g. KSK-01L with a boiling point of 330°C
330 (product name) is used.

The heat recovery circulation system 6 is configured so that the temperature of the heat medium flowing into the heat exchanger 3 is maintained at a temperature, for example, 130° C. or higher, which does not cause low-temperature corrosion in the heat exchanger.

FIG. 2 shows a more detailed configuration in which a circulation pump unit γ and a heat medium expansion tank 8 are interposed in the heat recovery circulation system 6 described above.

As shown in FIG. 2, the circulation pump unit γ includes two pumps γa and 1b arranged in parallel, a controllable three-way valve 1c communicating with the discharge ports of these pumps, and discharge ports of the pumps 1a and γb. and the first discharge port of the three-way valve 1c, the first discharge port of the three-way valve, the discharge port of the bypass valve BV, and the discharge port of the heat exchanger 5, respectively. It consists of a mixing chamber γd having two communicating inlets and an outlet communicating with the heat medium inlet of the steam heat exchanger 4.

The heat exchanger 3 is the same or different type of indirect heat exchanger 3a, 3b
and 3c.

This heat exchanger 3 is shown diagrammatically, and the exhaust gas passing through the heat exchanger 3 flows from left to right in FIG. 2 as indicated by the arrows.

The steam heat exchanger 4 has a heat exchanger 4a for heating a heat medium.
The steam injection space 4al in the tank 4a is connected to the waste heat boiler 2b via a controllable valve 4b, and the heat medium heating chamber 4a in the tank 4a is connected to the waste heat boiler 2b.
2 to the outlet of the mixing chamber γd as described above;
The heat medium heating chamber 4a3 is communicated with the inlet of the heat load device 5, while a temperature indicating controller (TIC) 4c is connected to the outlet of the heat medium heating chamber 4aa.

The output of the controller TIC is connected to the control input of the controllable valve 4b, and the opening degree of the valve 4b is adjusted by its output signal.

In addition, the output of the controller 'I' I C is controlled by a three-way valve 1.
The three-way valve γC is controlled by its output signal.

In addition, a pressure indicating controller PIC10 is connected to the feed line 9 from the steam heat exchanger 4 to the heat load device 5, and the controller P
The output of the IC is connected to the control input of a controllable valve 12 interposed between the feed line 9 and the belt line 11 from the thermal load device 5 to the circulation pump unit γ.

Reference character BY not explained above.

BV is bypass valve, ■ is on-off valve, TG is thermometer, PG
is a pressure gauge, C is a trap, and LG is a level gauge.

The method of the present invention will be explained below using an example of an apparatus configured as shown in FIGS. 1 and 2.

The exhaust gas from the incineration path etc. 1 is vented to the waste heat boiler 2b after HCl gas is removed in the dry gas treatment means 2a.

The exhaust gas that has been exhausted after absorbing heat by the waste heat boiler 2b is removed and purified by the electric precipitator 2c.

The exhaust gas from the electrostatic precipitator 2c is generally discharged at a gas temperature of about 300°C, regardless of the type of incinerator or the like that is the exhaust gas generation source.

This exhaust gas transfers its retained thermal energy to the heat exchanger 3.
The temperature of the heat medium is lowered, and the heat medium is released into the atmosphere from the chimney 2d.

The heat medium is maintained in the heat recovery circulation system 6 at a temperature that does not cause low-temperature corrosion to the indirect heat exchanger 3, for example, 130 degrees Celsius or higher, and the heat is transferred from the circulation pump unit 7 (see Fig. 2). It is sent under pressure to the exchanger 3.

Therefore, the tube wall temperature of the indirect heat exchanger 3 is maintained at 150° C. or higher, and the heat exchanger 3 is prevented from undergoing low-temperature corrosion.

Therefore, there is no need to consider measures against low-temperature corrosion.

When the steam heat exchanger 4 is provided, the flow rate from the circulation pump unit γ to the heat exchanger 3 is regulated by a valve 7c controlled by its temperature indicating controller TIC4c.

In this control type, when the inflow rate from the controllable valve 4b is zero or the valve 4b is set to a predetermined flow rate, the controller 4
The flow rate into the heat exchanger 3 is adjusted while the bypass flow rate from the valve γC to the mixing chamber 1d is adjusted by the valve 1c under the control of the valve 1c, and under such regulation, the bypass flow rate becomes zero [ When the discharge port of the valve 1c to the mixing chamber 1d is fully closed, the opening degree of the valve 4b is adjusted by the controller 4c to control the flow rate of the heat medium to the heat exchanger 3 and to supply liquid to the heat exchanger 3. This control is performed so that the steam type heat exchanger 4c compensates for the thermal deficiency in a state where the maximum possible flow rate of the heat medium is supplied to the heat exchanger 3.

In this way, the flow rate of the heat medium supplied to the heat exchanger 3 is variably adjusted to control the amount of heat exchanged.

If the amount of heat exchanged by the heat exchanger 3 is at its maximum and the amount of heat is further insufficient, the heat medium is further heat exchanged with the steam vented to the heat exchanger 4, and a high level of heat is generated. Becomes a medium.

By adjusting as described above, it is possible to variably adjust the amount of heat exchanged, in other words, it is possible to cope with fluctuations in heat load, and at the same time, the boiling point of the heating medium can be adjusted to the exit temperature of the electrostatic precipitator (generally 30°C).
Since a heat medium with a temperature higher than 0°C (approximately 0°C) is passed through the heat exchanger, there is a risk that the heat medium may evaporate and abnormally increase the pressure in the heat recovery circulation system 6 when the heat load is minimal or zero. Not at all.

Also, as described above, the heat medium brought to a high thermal level by the heat exchanger can be used for multiple purposes.

As the heat load device, for example, an absorption chiller, an absorption chiller/heater, a water heater, or a fluorocarbon turbine can be used, and the thermal energy can be used for air conditioning, heating, and power generation.

The heat medium that has been thermally elevated in the heat exchanger 3 is transferred to the valve I.
If it is bypassed at C, it is mixed with the thermally lower level heat medium in the mixing chamber γd and sent to the auxiliary heat exchanger 4 that may be used.

If a heat exchanger 4 is optionally included in the heat recovery circuit 6, it is used to increase the thermal level of the heating medium in a controlled manner as described above.

If auxiliary heat exchanger 4 is not required, bypass valve B
All you have to do is open the valve V1 and close the valve ■.

Furthermore, when the pressure in the feed path 9 leading to the heat load device 5 rises above the allowable pressure of the heat load device 5, the pressure indicating regulator 11 works to control the valve opening of the valve 12, thereby preventing an abnormal pressure rise. Protects the heat load device 5 from

Further, the temperature of the heat medium flowing into the heat exchanger 3 can be adjusted by using the heat recovery circulation system and/or the temperature control branch point, with or without providing a temperature control branch point in the heat recovery circulation system. This can be accomplished by controlling the

As is clear from the above description, the present invention exhibits the following excellent effects.

(1) Low-temperature corrosion can be prevented.

(2) Dust in exhaust gas can be prevented from adhering to the heat exchanger as much as possible, and corrosion due to dust adhesion can be prevented.

(3) Multipurpose use of heat can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a diagram showing the heat recovery circulation system in more detail. In the figure, 1 is an incinerator, etc., 2 is an exhaust gas treatment passage, 3 is a heat exchanger, 5 is a heat load device, and 6 is a heat recovery circulation system.

Claims (1)

[Scope of Claims] 1. A method for recovering heat from exhaust gas in an exhaust gas treatment system such as an incinerator, which includes providing a heat exchanger between the exhaust gas and a heat medium downstream of an electrostatic precipitator in the exhaust gas treatment system, and A heat recovery circulation system is configured to recover heat from the heat medium after heat exchange and return it to the heat exchanger, and the heat medium whose boiling point is higher than the exhaust gas temperature of the electrostatic precipitator is circulated within the heat recovery circulation system. A method for recovering heat from exhaust gas, which is characterized by recovering heat from exhaust gas. 2. Heat recovery from exhaust gas according to claim 1, characterized in that the temperature at which the heat medium flows into the heat exchanger is maintained at a temperature higher than a temperature that does not cause low-temperature corrosion in the heat exchanger. Method.