JP2001050109A - Cogeneration system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent occurrence of excessive temperature rise of catalyst caused by catalyst combustion and thermal damage of an exhaust heat recovery part, by using a lean combustion type gas engine so as to reduce NOx, in the case of removal of unburnt gas which is likely to form the lean combustion type engine with the use of an oxidation catalyst. SOLUTION: In a cogeneration system in which an oxidation catalyst device 4 is provided in an exhaust gas passage 3 extending from a gas engine 1 to an exhaust heat recovery part 2, a cooling air supply pipe 7 is merged into the passage 3 upstream of the oxidation catalyst device 4, through the intermediary of a regulating valve 5, and is incorporated therein with temperature sensors 8a, 8b for detecting a temperature of the catalyst device 4. With this arrangement, cooling air is fed into the exhaust gas passage 3 while the volume thereof is changed in accordance with outputs form the sensors 8a, 8b.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cogeneration system using a lean-burn gas engine.

[0002]

2. Description of the Related Art In recent years, a cogeneration system using a lean-burn gas engine 1 has been developed. Since a lean gas engine has excellent low NOx performance, if it can be used in a cogeneration system, an expensive NOx reduction device can be omitted. When adopting, there were the following problems. That is, the lean gas engine 1 has a very low NOx performance without generating a local high-temperature portion in the flame because the combustion gas is lean, but the unburned gas in the exhaust gas because the combustion is slow. This tendency is remarkable particularly at the time of starting or at the time of load transfer, where misfiring is likely to occur due to an ignition error. If an ignition source such as a reheating burner 4 is provided in the exhaust heat recovery boiler 3, there is a risk that the unburned gas may cause an explosion in the boiler 3 or the exhaust duct 5.

Therefore, as shown by a dotted line in FIG. 3, the present inventors interposed an oxidation catalyst 4 in the exhaust gas passage 3 of the lean gas engine 1 and catalytically burned unburned gas to thereby remove the unburned gas from the exhaust gas. An attempt was made to remove it. As the oxidation catalyst 4, for example, a porous alumina body formed into a honeycomb shape or a catalyst in which a platinum-based active metal is supported on alumina is used. According to this method, there is no possibility of discharging unburned gas to the outside, and the reburning burner 1
Even if an ignition source such as 3 is provided, there is no danger of explosion, and there is an advantage that heat generated by catalytic combustion is recovered by the exhaust heat recovery unit 2 without waste and energy efficiency is improved.

[0004]

However, the system shown in FIG. 3 has a problem that the oxidation catalyst 4 is deteriorated when the temperature of the exhaust gas becomes too high. Since it is converted into heat by combustion, not only the oxidation catalyst 4 is deteriorated, but also the exhaust heat recovery unit 2 may be adversely affected, for example, the brazing part of the boiler is thermally damaged. There was a problem. Therefore, the present invention solves the problems of the deterioration of the oxidation catalyst and the heat damage of the exhaust heat recovery unit 2 by a very simple configuration, and realizes a low-NOx and low-cost cogeneration system using a lean gas engine. It is intended for.

[0005]

As shown in FIG. 1, in the cogeneration system according to the present invention, an oxidation catalyst device 4 is interposed in an exhaust gas path 3 from a lean burn gas engine 1 to an exhaust heat recovery section 2. Exhaust gas path 3 upstream of the oxidation catalyst device 4 in the cogeneration system
The cooling air supply pipe 7 via the regulating valve 5 and a temperature sensor 8 a for detecting the temperature of the oxidation catalyst 4.
8b, the cooling air is increased or decreased in accordance with the outputs of the temperature sensors 8a and 8b, and is joined to the exhaust gas path 3. The unburned gas in the exhaust gas of the lean gas engine increases. Also in this case, it is characterized in that deterioration of the oxidation catalyst 4 due to excessive temperature rise or thermal damage to equipment such as a boiler in the exhaust heat recovery unit 2 can be prevented.

[0006]

FIG. 1 shows an embodiment of a cogeneration system according to the present invention.
A lean burn type is used. An oxidation catalyst device 4 is interposed in an exhaust gas path 3 from the gas engine 1 to the exhaust heat recovery unit 2, and unburned gas generated from the lean gas engine 1 is Catalytic combustion is performed on the oxidation catalyst 4. On the upstream side of the oxidation catalyst device 4, a cooling air supply pipe 7 is connected to the exhaust gas path 3 so as to merge with the exhaust gas path 3, and supplies outside air to the cooling air supply pipe 7 to cool the oxidation catalyst. And a motor-operated adjusting valve 5 for adjusting the amount of air. In the present embodiment, the air supply pipe 7 provided with the regulating valve 5 and the blower 6 is provided in two systems, one for always-on operation (# 1) and the other for emergency operation (# 2). Is to reduce the size and cost.

The temperature sensors 8a and 8b are provided near the inlet and the outlet of the catalyst 4, respectively.
The inlet temperature sensor 8a estimates the temperature rise in the catalyst,
The temperature of the exhaust gas from the engine must be constant (350 ° C)
It is for dilution with cold air at the time of above
The outlet temperature sensor 8b is also for blowing cooling air when the temperature of the catalyst becomes excessively high (390 ° C. or more) due to an abnormal increase in the amount of unburned gas. In the figure, 10 is a silencer, 11 is a manual butterfly valve, and 12 is a bypass valve.

FIG. 2 shows an example of the operation according to the configuration of the present invention.
At (t ₀ ), the # 1 blower starts to operate (t ₁ ), and at the same time, the # 1 regulating valve is fully opened, and the time required to bring the catalyst outlet temperature Tb to 300 ° C. or lower (if high) is obtained. After elapse, the engine is started (t ₂ ). Since a large amount of unburned gas is generated at the start of the operation, the # 1 blower is fully opened to dilute the unburned gas with air to prevent the catalyst temperature from rising. After a lapse of a predetermined time for the operation to stabilize and reduce the amount of unburned gas, the # 1 regulating valve is closed once (t ₃ ), and thereafter the normal operation is started. 8b
ON / OFF control is performed in accordance with the output signal from the CPU. This control is performed in two stages, and when the catalyst temperature rises sharply, the # 2 regulating valve and the # 2 blower are also switched to the outlet temperature Tb.
> 400 ° C.) also participates in cooling the catalyst (t ₄ ). If stopping the engine also, since first unburned gas when the load is reduced is increased, for example, when it becomes the engine output 30% (t _5), fixed time # 1 and # 2 control valve is fully opened At the same time, both blowers are operated, and thereafter (t ₆ ), air is blown only by the # 1 blower until the catalyst outlet temperature falls to Tb <300 ° C. (t ₇ ).

[0009]

According to the present invention, as described above, the catalytic combustion device 4 is interposed in the exhaust gas path 3 from the lean burn gas engine 1 to the exhaust heat recovery section 2 to remove unburned gas contained in the exhaust gas. Catalytic combustion prevents exhaust to the outside and increases the amount of exhaust heat recovery.In addition, the problem of deterioration due to excessive temperature rise of the oxidation catalyst at that time, and emission due to catalytic combustion of all unburned gas. There is an advantage that the problem of thermal damage to the heat recovery unit 2 can be solved with a very simple and inexpensive configuration in which cooling air is blown into the oxidation catalyst.

[Brief description of the drawings]

FIG. 1 is a system diagram of one embodiment of the present invention.

FIG. 2 is a time chart showing an example of the above operation.

FIG. 3 is a system diagram of a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Lean gas engine 2 Exhaust heat recovery part 3 Boiler 3 Exhaust gas path 4 Oxidation catalyst device 5 Regulator valve 6 Blower 7 Air supply pipe 8a Temperature sensor 8b Outlet temperature sensor 8a Inlet temperature sensor 9 Control device 10 Silencer 11 Manual butterfly valve 12 Bypass Valve Tb outlet temperature Tb Catalyst outlet temperature

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Hidehiko Kobayashi 4-1-2, Hirano-cho, Chuo-ku, Osaka-shi F-term in Osaka Gas Co., Ltd. (reference) 3G091 AA06 AA12 AA19 AB02 BA05 BA08 BA10 BA15 BA19 BA36 CA08 CA13 CA23 DA01 DA02 DA03 DB10 EA17 EA18 FB10 HA04 HA36 HA37 HA38 HA42 HB03 HB07 3K065 TA08 TC07 TD05 TK02 TK04 TK06 TL01 TM05 TN01

Claims (1)

[Claims] In a cogeneration system in which an oxidation catalyst device is interposed in an exhaust gas path from a lean burn type gas engine to an exhaust heat recovery unit, cooling is performed through an adjustment valve in an exhaust gas path upstream of the oxidation catalyst device. A cogeneration system comprising a temperature sensor for detecting the temperature of an oxidation catalyst while joining an air supply pipe, and joining the cooling air to the exhaust gas path while increasing or decreasing the cooling air according to the output of the temperature sensor.