JPH0612161B2 - Heat recovery device for boiler exhaust gas - Google Patents

Description

TECHNICAL FIELD The present invention relates to a heat recovery device for exhaust gas of a boiler that burns a high water content fuel such as pulp sludge, precipitated pulverized coal or other low grade coal.

[Conventional technology]

Conventionally, a economizer and a gas type air preheater have been installed in order to recover the sensible heat of exhaust gas as much as possible and improve the boiler efficiency. Conventionally, the heat recovery device has generally been installed according to the flow shown in FIG. That is, in the exhaust gas line 4 of the boiler 1 for burning the high water content fuel, the economizer 2 is provided upstream and the gas air preheater 3 is provided downstream in series. 5 is a chimney.

Further, conventionally, as shown in FIG. 5, a method has also been used in which an exhaust gas line 4 of a boiler 1 is provided with a gas type air preheater 3 in the upstream side and a economizer 2 in series in the downstream side.

Further, JP-A-58-64404 discloses a boiler exhaust gas heat recovery system in which an exhaust gas / air heater and an exhaust gas / blast furnace gas heater are arranged in parallel in an exhaust gas line of a boiler that burns low-calorie gas such as blast furnace gas. Is listed.

In JP-A-60-105819, exhaust gas from a coal-fired boiler is burned with a primary air preheater that preheats the primary air that is the air for drying the coal and transporting it into the boiler. For feeding secondary air to the secondary air preheater for heating in parallel.

[Problems to be Solved by the Invention]

In the case of a high water content fuel, it is generally necessary to raise the temperature of the combustion air for stable combustion. Further, the ratio of the amount of air passing through the gas type air preheater 3 to the amount of gas is about 1: 1 for general fuels such as heavy oil and coal, while it is around 1: 2 for high water content fuels. May reach. In this case, the 4th
As shown in the figure, when the gas type air preheater 3 is installed on the downstream side in an attempt to recover heat, the gas type air preheater outlet gas temperature is changed due to the balance of gas and air in the gas type air preheater. Therefore, the exhaust gas loss is increased, and a large amount of energy is lost, resulting in a decrease in thermal efficiency.

Therefore, in the case of a boiler that burns a high water content fuel, as shown in FIG. 5, a system in which the gas type air preheater 3 is installed on the upstream side and the economizer 2 is installed on the downstream side is adopted.

However, in the case shown in Fig. 5, in order to improve the thermal efficiency (lower the exhaust gas temperature), it is necessary to lower the feed water temperature at the inlet of the economizer, which results in low-temperature corrosion and long equipment. There is an inconvenience that it cannot be used stably for a period.

Further, in JP-A-58-64404, the blast furnace gas is the fuel, and in JP-A-60-105819, the low-moisture coal that can be dried with gas is the fuel, and both have a water content of 30% by weight. The above high water content fuel is not used as a fuel.

The present invention has been made in view of the above points, and the water content
In boilers handling high water content fuel of 30% by weight or more,
It is an object of the present invention to provide a heat recovery device that is free from the concern of low temperature corrosion of a economizer and can improve thermal efficiency.

[Means and Actions for Solving the Problems]

The boiler exhaust gas heat recovery apparatus of the present invention will be described with reference to FIG. 1. In the exhaust gas line 4 of the boiler 1 for burning a high water content fuel having a water content of 30% by weight or more, a economizer 2 and a gas are provided. It is characterized in that the air preheater 3 is connected in parallel.

As the high water content fuel, use pulp sludge, precipitated pulverized coal or other low grade coal with a water content of 30% by weight or more.

The exhaust gas enters the economizer 2 and the gas type air preheater 3 in parallel, and heat is recovered to a temperature as low as possible. On the other hand, the boiler feed water enters the economizer 2 at a temperature at which there is no fear of low temperature corrosion, the sensible heat of the gas is obtained, the temperature rises, and the boiler 1 is supplied to the boiler 1. Further, the air enters the gas type preheater 3 and obtains the sensible heat of the gas to reach the temperature required for the combustion of the high water content fuel.
Is supplied to.

〔Example〕

Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to FIG. However, the shape of the components described in this embodiment, its relative arrangement, etc., unless otherwise specifically stated, is not intended to limit the scope of the present invention only to them, but to a mere explanation example. Not too much.

As shown in Fig. 1, the boiler 1 that burns high water content fuel
The economizer 2 and the gas type air preheater 3 are connected in parallel to the exhaust gas line 4. 5 is a chimney.

The exhaust gas from the boiler 1 is used as the economizer 2 installed in parallel.
Then, the heat enters the gas type air preheater 3, the heat is recovered to a temperature as low as possible, and the heat is discharged from the chimney 5. On the other hand, the boiler feed water enters the economizer 2 at a temperature at which there is no risk of low temperature corrosion, where the sensible heat of the gas is obtained and the temperature is raised, and the boiler 1 is supplied to the boiler 1. Further, the air enters the gas type air preheater 3, similarly obtains sensible heat of the gas, is heated to a temperature required for combustion of the high water content fuel, and is supplied to the boiler 1.

Since the heat recovery devices are arranged in parallel as described above,
When the dust adhesion state to both heat recovery devices is different or the load changes, an imbalance in the gas flow rate to both heat recovery devices occurs,
Disturbance for optimal driving. In order to cope with this, the dampers 6 and 7 are respectively provided on the downstream side of the heat recovery device, and the dampers are adjusted, so that the optimum operation can be continued.

Next, examples and calculation examples will be described. A boiler that uses pulp sludge as a fuel, and the water content of the fuel is approximately 65%. Other planned conditions for the boiler are an atmospheric temperature of 20 ° C and a feedwater temperature at the economizer inlet of 150 ° C. The combustion air volume is 60,000 Nm ³ / H
310 ℃ is required, and the amount of exhaust gas is 100,000Nm ³ / H.

FIG. 4, that is, the balance around the gas type air preheater in the case where the gas type air preheater 3 is installed is as shown in FIG.

Generally, in a heat exchanger, the temperature difference between the heated object (here, gas) and the object to be heated (here, air) is at least 30 ° C considering the economic efficiency of the heat exchanger and the heat exchange balance at low load. Air preheater inlet gas temperature is 34
As a result, the outlet exhaust gas temperature is 174 ° C.
Becomes

In addition, in FIG. 5, that is, in the case where the economizer 2 is installed later,
Since the inlet feed water temperature is 150 ° C, the exhaust gas temperature is at least 180 ° C from the above point, and the exhaust gas temperature is higher than the case of Fig. 4, so the comparison with the present invention is the case of Fig. 4. To do.

In the case of the present invention, as shown in FIG. 2, the gas amount is 100,000 Nm ³ /
H in the 75,000 ³ / H of the gas of the 3/4 gas type air preheater 3 side and flowed 1/4 of 25,000 ³ / H of the gas to the fuel economizer 2 side.

As in the case of FIG. 4, in order to secure the outlet air temperature of the gas type air preheater of 310 ° C., the gas type air preheater outlet gas (exhaust gas) temperature is 119 ° C. On the other hand, the outlet gas temperature of the economizer should be at least as low as the heat exchanger temperature difference described above.
180 ° C. As a result, the temperature of the mixed gas at the outlets of both heat exchangers was 134 ° C, and the exhaust gas temperature was 40% compared to the case in Fig. 4.
C lowers.

This decrease in exhaust gas temperature increases boiler efficiency by 4.6% (7
6.5% → 81.1%). Converting this to a boiler evaporation rate, in the case of FIG. 4, the steam generation rate is 35 T / H, but when using the device of the present invention, the steam generation rate is
It becomes 37.1T / H. Converting this 2.1T / H evaporation increase into heavy fuel oil, which is a general fuel, 1,2
It saves 00 ^{TON /} year, resulting in significant energy savings.

〔The invention's effect〕

Since the present invention is configured as described above, it is possible to prevent low temperature corrosion in a heat exchanger of a boiler using a high water content fuel as a fuel and to significantly improve boiler efficiency. is doing.

[Brief description of drawings]

FIG. 1 is a flow sheet showing an example of a boiler exhaust gas heat recovery apparatus of the present invention, FIG. 2 is a flow sheet showing an exhaust gas flow rate in an embodiment of the present invention, and FIG. 3 is a gas in a conventional example shown in FIG. FIG. 4 and FIG. 5 are temperature diagrams showing the temperature balance around the air preheater, and are flow sheets showing a conventional example. 1 ... Boiler, 2 ... Coal saver, 3 ... Gas type air preheater, 4 ...
Exhaust gas line, 5 ... Chimney, 6, 7 ... Damper

Claims (1)

[Claims] 1. A economizer (2) and a gas type air preheater (3) are connected in parallel to an exhaust gas line (4) of a boiler (1) for burning a high water content fuel having a water content of 30% by weight or more. Boiler exhaust gas heat recovery device characterized by being connected.