JPS58173397A - Waste heat recovery method of corrosive gas - Google Patents

Abstract

PURPOSE:To prevent sulfurous acid and sulfuric acid from being formed on tube wall and consequently prevent the tube wall from being corroded by a method wherein the temperature of the tube wall of heating part is controlled within a predetermined temperature range above dew point regardless of the change of exhaust gas temperature. CONSTITUTION:When the temperature of exhaust gas stream 1 falls down too much due to the cause such as load change or the like, a temperature detector 20 provided at exhaust gas outlet side issues a signal in order to actuate a flow control valve 11 to close, resulting in causing the decrease of the amount of pure water circulating in the radiating part 5 and then the temperature rise in the radiating part 5. Because the temperature of the tube wall of the heating part 3 rises accompanying with said temperature rise in the radiating part 5, the temperature of the tube wall can be controlled above acid dew point. In this case, the flow rate in a by- pass 10 increases, resulting in causing to lower the temperature of a feed water heater 9. On the contrary, when the temperature of exhaust gas rises too much, the flow control valve 11 is actuated to open itself by the signal issued from the detector 20, resulting in causing the circulation of a large amount of pure water in the radiating part 5 and then the lowering of the temperature in the radiating part 5 and the consequent lowering of the temperature of the tube wall of the heating part 3. In this time, the flow rate in the by-pass 10 decreases, resulting in causing to raise the temperature of the feed water heater 9. In such a manner as described above, the temperature of the tube wall of the heating part 3 of a heat pipe is controlled above acid dew point, resulting in preventing the tube wall of the heat pipe from being corroded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of recovering waste heat from exhaust gas from boilers, industrial furnaces, etc. containing corrosive gases such as SOx using a heat pipe.

Traditionally, economizers have been used to recover heat from boiler exhaust, but even if the combustion exhaust gas comes into direct contact with water pipes, the heat capacity of the water is large, so water pipes are used! Ti! ii) The temperature does not rise much above 1 degree, and acid may condense on the tube wall.

Generally, the tube wall temperature is expressed by the following formula.

Tw = T-(r-t) - Tw: Pipe wall temperature T: Exhaust gas temperature t: Water supply inlet temperature R: Overall heat transfer resistance value r: Tube inside heat transfer resistance value, for example, 20°C for feed water and 200°C for exhaust gas But the tube wall temperature I
/'i stays around 50℃, sOx acid dew point 110 ~
At temperatures below 150℃, woodwinds corrode due to sulfurous acid and sulfuric acid. Conventionally, measures have been taken to prevent such corrosion, such as using corrosion-resistant materials for the wood pipes or raising the temperature of the exhaust gas, but these methods increase production costs and are undesirable from an energy-saving standpoint.

On the other hand, in heat pipes, the inner wall of the sealed pipe is coated with water, fluorocarbons, and benzene.

A working fluid of suitable wax such as Ayaton, ammonia, alcohol, etc. is sealed and vaporized at both ends of the tube.

The RM phase conversion cycle is utilized to transport heat between high and low temperatures. The thermal energy exchanged during phase conversion of the working fluid is smaller than that of heat transfer, and has the advantage of being able to transfer a large amount of thermal energy. Both ends of this heat pipe are isolated and exchange heat with different fluids, so the heat dissipation part on the low temperature side at one end of the heat pipe does not come in contact with the SOx atmosphere, so there is no risk of acid condensation. Even if the heat receiving section at the end is in high temperature exhaust gas, the temperature of the tube wall may be influenced by the temperature of the heat dissipating section and exceed the acid dew point.

When recovering waste heat from high-temperature exhaust gas containing SOx, the present invention uses a heat pipe to absorb a large amount of thermal energy into a toothed heating medium, and causes corrosion by causing the heating medium to exchange Ta with supplied water. Collect waste heat indirectly from exhaust gas,
Prevents corrosion caused by conventional economizers, yet has only one outlet
It is possible to detect the exhaust gas temperature and adjust the amount of heat medium to keep the tube wall temperature of the heat pipe heat receiving part above the V dew point at all times, to prevent overcooling of the heat medium, and to ensure smooth startup. An embodiment thereof will be explained below with reference to the accompanying drawings.

A heat receiving part 6 of a heat pipe 2 is located in a high-temperature exhaust gas flow 1 containing SOx, and a heat radiating part 5 is provided in a continuous circuit 6 through which a heat medium such as pure water flows, with a partition wall 4 in between. This (I1
1 circuit 6 is equipped with the heat pipe heat dissipation section 5, an expansion tank 7, a toothed ring pump 8, a multi-tube feed water heater 9, a bypass pipe 10, a flow rate control valve 11, and a steam blowing pipe. 12 are in contact.

In the apparatus configured as described above, for example, 5Oxt
The exhaust gas containing about 250 to 280 degrees Celsius passes through the heat receiving part 3 of the heat pipe, exchanges heat with the working fluid, and is then discharged from the outlet side 13 at a temperature of about 150 to 180 degrees Celsius, and the working fluid vaporizes and radiates heat. Thermal energy is transferred to part 5 to give heat to the pure water in the painting stage, where it condenses itself and returns to the heat receiving part 5 after passing through the water, and this process is repeated.

The pure water, which undergoes heat exchange in the heat radiating section 5 and is heated to about 120 to 150° C., reaches the expansion tank 7. This expansion tank 7 has a pure water replenishment pump 14 and a near compressor 15, and the near compressor 15 is operated as necessary to pressurize the pure water and prevent cavitation of the III pump 8.

The pure water that has passed through the expansion tank 7 is
After being pressure-fed to the multi-tube feed water heater 9 and exchanging heat with about 20 to 400 feed water introduced from the inlet pipe 16, about 1
It passes through the tube 17 at a temperature of 10 to 140°C. Through this heat exchange, the feed water recovers all waste heat, is heated to about 80 to 120° C., and is taken out from the outlet pipe 18 and used, for example, as boiler feed water. Valve 21 is for overload adjustment.

A portion of the pure water passing through the pipe 17 is diverted to the bypass pipe 10 having the pulp 19t' and introduced into the inlet side of the bacterial ring pump 8, and the remainder passes through the flow control valve 11 and then flows into the bypass pipe 10 containing the pulp 19t'.
When the temperature reaches 0° C., the heat pipe returns to the heat dissipating section 5 and is beamed again.

Here, if the temperature of the exhaust gas airflow 1 drops too much due to a cause such as load fluctuation, the temperature detector 20 installed on the wandering gas outlet side issues a signal, the flow rate control valve 11 operates in the closing direction, and the heat dissipation section Since the amount of purified water circulating in 5 decreases, the temperature of the heat dissipating section 5 increases, and the temperature of the tube wall of the heat receiving section 5 increases accordingly.
The temperature rises to above the acid dew point and starvation can be achieved. At this time, bypass pipe line 1
0 flow rate increases and the temperature of the feed water heater 9 decreases. reverse VC
#! : If the gas temperature rises too much, the flow control valve 11 is operated in the direction of opening by the signal issued by the temperature detector 20, and a large amount of pure water flows into the heat radiating part 5, and the temperature of the heat radiating part 5 decreases, so that the heat receiving part 6, the tube wall temperature decreases. At this time, the flow rate of the bypass pipe 10 decreases, and the temperature of the feed water heater 9 increases. In this way, the temperature of the tube wall of the heat pipe heat receiving section 5 can be controlled to be higher than the acid dew point, thereby preventing corrosion of the heat pipe tube wall.

A steam inlet pipe 12 connected to the loop circuit 6 prevents overcooling of the circulating pure water caused by rapid load fluctuations and serves to heat the pure water at the start of operation.

Although pure water was used as the heating medium in the above examples, oil was used as the heating medium.

Other heat media can also be used, and electric thermal power or the like can also be used as an external heat source.

The present invention detects the exhaust gas outlet temperature and adjusts the flow rate of the heavy ring heating medium when the thermal energy retained in the corrosive exhaust gas absorbed by the heat receiving part of the heat pipe is released to the heating medium passing through the heat radiating part. This is a corrosive gas waste heat recovery method characterized by controlling the tube wall temperature of the heat pipe heat receiving part within a predetermined wet coal range above the acid dew point. Furthermore, since a heating medium is used, there is no need to worry about oxidation when heating boiler feed water. Also, the combination of such a heat pipe, a heating medium that decomposes, and a flow rate control valve reduces exhaust gas emissions. If the temperature drops too much, the heat medium flow fine adjustment mechanism operates in the direction of closing and reduces the heat medium flow rate, causing the temperature of the heat pipe heat dissipation section to rise, and the temperature of the tube wall of the heat receiving section to decrease accordingly. If the temperature of the exhaust gas exceeds the acid dew point temperature, and conversely the exhaust gas temperature rises too much, the flow control valve opens and the amount of heat transfer medium increases, and the heat radiating section becomes low temperature, causing the total temperature of the heat receiving section tube wall to drop. Regardless of fluctuations in exhaust gas, the temperature of the tube wall of the heat receiving section can be controlled within a predetermined wet coal range above the dew point temperature, and the tube wall is free of sulfur dioxide.

No sulfuric acid is generated and corrosion can be prevented. Therefore, the heat pipe does not need to be corrosion resistant, the manufacturing cost is low, and there is no need for 1 kFi of reheating the exhaust gas as in the past, which is advantageous in terms of energy. In addition, if an external heat source is connected to the heating medium VTI ring circuit, overcooling of the heating medium can be prevented and the tube wall temperature in the heat pipe heat dissipation section can be prevented from decreasing. It also has the effect of quickly returning to normal operation.

As described above, in the present invention, since there are no corroded parts during waste heat recovery, operation management becomes easy over a long period of time, and reliability is high.

[Brief explanation of drawings]

The figure is a flow sheet in one embodiment of the present invention. 1... High-temperature exhaust gas flow 2... Heat pipe 3... Heat receiving section 4... Partition wall 5... Heat radiation section 6
...Art world circuit 7...Expansion tank 8...C
Item 1 Pump 9...Multi-tube water heater 10...
Bypass pipe line 11...Flow rate control valve 12...Steam blowing pipe 15...Outlet side 14...Pump for pure water replenishment 15...Near compressor 20...Temperature detector patent applicant Sasafumi Co., Ltd. machine shop

Claims (1)

[Claims] When the thermal energy retained in the corrosive exhaust gas absorbed by the heat receiving part of the heat pipe is released to the heat medium that passes through the heat radiating part and breaks down, the exhaust gas outlet temperature is detected and the flow rate of the chain ring heat medium is adjusted. A corrosive gas waste heat recovery method characterized by controlling the temperature of the pipe wall of the heat receiving part of the pipe to be higher than the acid dew point.