JPH10159575A - Operating method for full fired heat recovery combined cycle system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate a boost-up fan, and reduce a cost of a device by setting back pressure of a supercharger to back pressure capable of leading exhaust gas into a boiler in a condition in which pressure in a boiler is positive pressure, in a device formed in such a constitution that exhaust gas is mixed with air for combustion and is supplied to the boiler. SOLUTION: At the time of operation of this system, exhaust gas delivered from a diesel engine 2 is mixed with combustion air supplied from a forced draft fan 4 after it is fed to a mixer of a boiler 1, and is supplied for combustion in the boiler 1. In this time, an operation is carried out in such a way that back pressure of a supercharger 21 is matched with back pressure higher than that of a maximum efficiency point of the supercharger 21 so as to make back pressure capable of leading exhaust gas into the boiler 1 in a condition in which pressure of the boiler 1 is in a positive pressure condition. Pressure in the boiler 1 not make negative pressure even if pressure loss is generated in the boiler 1, and exhaust gas bypassing the supercharger 21 is led to the boiler l without using a boost-up fan.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for operating an exhaust gas reburning combined cycle system in which exhaust gas from a turbocharged diesel engine is mixed with combustion air and sent to a boiler.

[0002]

2. Description of the Related Art In a power plant, various exhaust refueling combined systems are used in which exhaust gas from a diesel engine is mixed with air for combustion into a boiler and supplied to the boiler.

FIG. 2 is a system diagram showing one example of a conventional exhaust refueling combined system. In FIG. 2, 1
Is a boiler, 2 is a diesel engine, 21 is a supercharger, 3 is a boost-up fan for increasing the pressure of exhaust gas discharged from the diesel engine 2, and 4 is a for supplying combustion air to the boiler 1. The push-in fan 5 is a suction fan.

[0004] In such an exhaust gas reburning combined cycle plant, the supercharger 21 driven by the exhaust gas of the diesel engine 2 usually has an allowable back pressure Pa = 200 m.
Matching is performed at about mAq. FIG. 3 shows a performance curve (matching line) of the supercharger 21 for the large diesel engine 2.
The matching between the supercharger 21 and the diesel engine 2 is such that the highest engine performance can be exhibited with respect to the design output of the diesel engine 2 equipped with the supercharger 21, that is, the supercharger efficiency is maximized. ing.

In general, as shown in FIG. 3, the efficiency of the supercharger 21 increases as it approaches the surging line. Therefore, the turbocharger 21 changes the setting of the turbine nozzle and the diffuser so as to be as close as possible to the surging line. Then the matching is done. At this time, if the back pressure of the turbocharger is changed, the surging line moves, so that the matching point changes.

[0006] Even if the furnace pressure in the boiler 1 is controlled to be as small as possible, for example, 0 mmAq, due to the above-mentioned supercharger characteristics, the pressure loss in the duct and the wind box of the air and exhaust gas supply system is reduced. For this reason, when the back pressure of the supercharger 21 is matched to be 200 mmAq as described above, the back pressure becomes too small, and it becomes difficult to smoothly introduce the exhaust gas into the boiler 1. The boost-up fan 3 is installed in the exhaust gas passage downstream of the feeder 21 to increase the pressure of the exhaust gas supplied to the boiler 1.

[0007]

As described above, in the conventional exhaust gas reburning combined cycle plant shown in FIG. 2, the back pressure of the supercharger attached to the diesel engine 2 is used to reduce the supercharger efficiency. In order to prevent the boiler furnace pressure from becoming negative after the pressure is set to about 200 mmAq from the surface, a boost-up fan 3 is provided to pressurize the exhaust gas and introduce it into the boiler.

For this reason, the above-mentioned boost-up fan 3 is required as plant equipment, which complicates the plant system and increases the equipment cost. Further, since the exhaust gas is used at the low turbocharger back pressure level as described above, the temperature of the exhaust gas introduced into the boiler 1 becomes low, so that the plant efficiency must be lowered.

An object of the present invention is to eliminate the need for a boost-up fan in the exhaust gas passage downstream of the supercharger, to simplify the structure while avoiding a decrease in plant efficiency, and to reduce the cost of the exhaust refueling combined cycle system. Another object of the present invention is to provide a driving method.

[0010]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and its gist is to mix exhaust gas from a turbocharged diesel engine with combustion air to produce a boiler. In the exhaust refueling combined cycle system, the back pressure of the supercharger is adjusted so that the back pressure is such that at least the furnace pressure of the boiler is a positive pressure and exhaust gas can be introduced into the boiler. The configuration is such that the matching operation is performed at a back pressure higher than the back pressure at the highest efficiency point of the supercharger.

In the above method, it is preferable to perform matching so that the back pressure of the supercharger is close to 500 mmAq.

According to this method, the back pressure of the supercharger is 50
Since the turbocharger and the diesel engine are matched so that the vicinity of 0 mmAq is higher than the conventional value of about 200 mmAq, even if there is a pressure loss in the exhaust duct or the wind box to the boiler, the pressure of the furnace of the boiler is reduced. The exhaust gas that has passed through the supercharger can be introduced into the boiler without using a boost-up fan as in the conventional case, by controlling so that the pressure does not become negative.

[0013] Although the efficiency of the turbocharger and the diesel engine decreases due to the increase in the back pressure, the temperature of the exhaust gas introduced into the boiler increases, and the amount of sensible heat of the exhaust gas recovered in the boiler increases. The efficiency of the whole plant does not decrease.

Therefore, according to the method of the present invention, it is possible to omit the boost-up fan like the conventional one without lowering the plant efficiency, and the apparatus is simplified and the cost is reduced.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to FIG. FIG. 1 shows a system diagram of an exhaust gas reburning combined system according to an embodiment of the present invention. In FIG. 1, 1 is a boiler, 2 is a diesel engine, 21 is a supercharger driven by exhaust gas of the diesel engine, 4 is a push-in ventilator for supplying combustion air to the boiler 1, and 5 is suction It is a ventilator.

In the embodiment of the present invention, the booster fan 3 in the conventional system shown in FIG. 2 is not provided, and the exhaust gas from the diesel engine 2 through the supercharger 21 is directly mixed in the boiler 1 (not shown). And mixed with the combustion air from the push-in fan 4.

That is, in this embodiment, the allowable back pressure of the supercharger 21 is set higher than the maximum efficiency point of the supercharger 5.
It is configured to perform matching with the diesel engine 2 by raising the pressure to about 00 mmAq. As will be described later, by performing the matching at such a high back pressure, the boiler can be provided without providing the boost-up fan 3. The exhaust gas can be introduced into the boiler 1 without the furnace pressure becoming negative.

During the operation of the exhaust refueling combined cycle system configured as described above, the exhaust gas discharged from the diesel engine 2 drives the supercharger 21 to pressurize the air supply to the engine 2. Thereafter, it is sent to a mixer (not shown) of the boiler 1. Further, the exhaust gas is mixed with combustion air which is supplied from the forced draft fan 4 and preheated by an air preheater (not shown), sent to a furnace of a boiler (not shown), and provided for combustion. .

In the above operation, the back pressure of the supercharger 21 is higher than that of the conventional system shown in FIG.
Since matching is performed so as to be in the vicinity of mmAq,
Even if there is a pressure loss in the exhaust duct or wind box to the boiler 1, the pressure in the furnace of the boiler 1 is controlled so as not to be a negative pressure (for example, by controlling the pressure to 0 mmAq or a slightly higher pressure). The exhaust gas that has passed through the feeder 21 can be introduced into the boiler 1 without providing a boost-up fan 3 (see FIG. 2) as in the conventional case.

For this reason, in the system according to the above-described embodiment, in the performance curve of the supercharger 21 shown in FIG. Since the surging line moves to the low efficiency side, the efficiency of the supercharger 21 and the diesel engine 2 decreases. However, due to the increase in the supercharger back pressure, the temperature of the exhaust gas at the outlet of the supercharger 21 increases, and the amount of sensible heat of the exhaust gas in the boiler 1 increases. Also, even if the efficiency of the diesel engine 2 is reduced, the plant efficiency of the entire exhaust-refueling combined system is not reduced.

Therefore, according to this embodiment, a boost-up fan like the conventional one can be omitted without lowering the plant efficiency, and the structure can be simplified and the cost of the apparatus can be reduced.

[0022]

The present invention is configured as described above.
According to the present invention, the supercharger is matched so that the back pressure is higher than the conventional one, so that even if the conventional boost-up fan is omitted, the furnace pressure of the boiler does not become negative. It is possible to control and introduce exhaust gas into the boiler. In addition, although the efficiency of the diesel engine and the turbocharger decreases due to the increase in the back pressure, the decrease in the plant efficiency due to the increase in the exhaust gas temperature can be avoided. Therefore, simplification of the plant structure and cost reduction by omitting the boost-up fan can be realized without observing a decrease in plant efficiency.

[Brief description of the drawings]

FIG. 1 is a system diagram of an exhaust gas reburning combined cycle system according to an embodiment of the present invention.

FIG. 2 is a diagram corresponding to FIG. 1 showing the conventional system.

FIG. 3 is a performance diagram of a supercharger.

[Explanation of symbols]

 Reference Signs List 1 boiler 2 diesel engine 4 push-in ventilator 5 suction ventilator 21 supercharger 3 boost-up fan (conventional example)

Claims (2)

[Claims] When operating an exhaust refueling combined cycle system in which exhaust gas from a turbocharged diesel engine is mixed with combustion air and supplied to a boiler, at least the back pressure of the supercharger is reduced. It is necessary to match and operate the supercharger at a back pressure higher than the back pressure at the highest efficiency point of the supercharger so that the furnace pressure of the boiler becomes a back pressure at which exhaust gas can be introduced into the boiler in a state of positive pressure. An operating method of the exhaust cycle combined cycle system, which is a characteristic feature. 2. The operating method of the exhaust refueling combined cycle system according to claim 1, wherein the matching is performed so that the back pressure of the supercharger is close to 500 mmAq.