JP2009036111A - Fuel change over method and fuel change over device for gas engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stably change over a high calorie gas and a low calorie gas and stabilize steady operation. <P>SOLUTION: A control device 7 sets a target value of air-fuel ratio of a gas engine and controls air-fuel ratio for the target value by a flow regulating valves 4A, 4B while controlling a supply quantity of a high calorie gas and a low calorie gas when fuel of a gas engine is changed over. The control device 7 carries out control to add a high calorie gas of an appropriate quantity to a low calorie gas when air-fuel ratio gets to a value insufficient for stable drive of the gas engine during operation of the gas engine with only the low calorie gas. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an apparatus for supplying a fuel gas to a gas engine, and more particularly to a fuel switching apparatus and a fuel switching method for switching and supplying a high calorie gas and a low calorie gas.

  In recent years, gas engines have been driven using biogas such as carbon monoxide obtained by pyrolyzing woody biomass such as methane gas generated from organic waste such as garbage, thinned wood, and construction waste in a gasifier. A system for generating electricity has been proposed.

  Biogas has a problem that its generation amount and components are likely to fluctuate and is low in calories, so that ignition when starting a gas engine is difficult. Therefore, after starting the engine with a high calorie gas such as propane gas and stabilizing the engine speed, a method of switching from high calorie gas to operation with a single low calorie gas has been devised (for example, Patent Document 1).

In switching from high calorie gas to low calorie gas, in Patent Document 1, after starting the engine with high calorie gas alone, the opening degree of the throttle valve for adjusting the flow rate of high / low calorie gas is set, and the opening degree After that, the low-calorie gas shut-off valve that was in the closed state is opened, the high-calorie gas shut-off valve that was in the open state is closed, and the start-up is completed.
JP 2004-293465 A

  As described above, when switching between high-calorie gas and low-calorie gas is instantaneously performed by each shut-off valve, the engine may misfire because the property of the gas flowing into the engine changes abruptly.

  As a countermeasure against this misfire, it is conceivable to gradually switch the gas flowing into the gas engine by operating the opening of two valves for adjusting the gas flow rate. However, if the gas switching amount is excessive or insufficient during the valve opening operation, switching failure due to misfire is caused. For example, in the middle of switching, if the increase in the low calorie gas flow rate does not satisfy the amount sufficient to maintain the operation of the gas engine with respect to the decrease in the high calorie gas flow rate, it will lead to misfire. In particular, biogas is unstable because its properties change abruptly, making switching operations difficult.

  In addition, the gas engine starts steady operation by supplying low calorie gas alone after starting, but the amount of biogas generated may be insufficient, and operation by low calorie gas alone cannot be maintained due to insufficient calories. The situation may continue or the amount of gas generated may be unstable, making stable operation difficult.

  An object of the present invention is to provide a fuel switching device and a fuel switching method for a gas engine that can stably switch between a high-calorie gas and a low-calorie gas and that can be stabilized during steady operation. .

In order to solve the above problems, the present invention sets an air-fuel ratio value within a range in which the gas engine can be driven as a target value of the air-fuel ratio, and provides high-calorie gas and low-calorie gas as fuel supplied to the gas engine. When switching, the fuel is switched while controlling the supply amount of both gases so that the air-fuel ratio becomes the target value, and if the air-fuel ratio that can stably drive the gas engine is not obtained during steady operation of the gas engine, low calorie An appropriate amount of high calorie gas is added to the gas, and is characterized by the following apparatus and method.
Note that the target value of the air-fuel ratio may be set as a numerical range.

(Invention of the device)
(1) A fuel switching device for a gas engine that shifts a gas engine driven by high-calorie gas to operation by a single supply of low-calorie gas,
A high calorie gas valve capable of shutting off and adjusting the flow rate of the high calorie gas supplied to the gas engine;
A low calorie gas valve capable of shutting off and adjusting the flow rate of the low calorie gas supplied to the gas engine;
A control device capable of blocking the valve and adjusting the flow rate;
The control device sets the target value of the air-fuel ratio of the gas engine, and switches the fuel of the gas engine while controlling the supply amount of the high calorie gas and the low calorie gas so that the air-fuel ratio becomes the target value. It is characterized by having a control means for switching between.

  (2) The control device includes control means for adding an appropriate amount of high-calorie gas to low-calorie gas when the air-fuel ratio becomes insufficient to stably drive the gas engine during operation of the gas engine using low-calorie gas alone. It is characterized by that.

  (3) The control means controls a gas supply amount by setting a target value of the air-fuel ratio to a theoretical air-fuel ratio.

  (4) The control means controls the gas supply amount by setting the target value of the air-fuel ratio to a value that is richer than the theoretical air-fuel ratio.

(Invention of method)
(5) A fuel switching method for a gas engine that shifts a gas engine driven by high-calorie gas to operation by a single supply of low-calorie gas,
A high calorie gas valve capable of shutting off and adjusting the flow rate of the high calorie gas supplied to the gas engine;
A low calorie gas valve capable of shutting off and adjusting the flow rate of the low calorie gas supplied to the gas engine;
A control device capable of blocking the valve and adjusting the flow rate;
The control device sets the target value of the air-fuel ratio of the gas engine, and switches the fuel of the gas engine while controlling the supply amount of the high calorie gas and the low calorie gas so that the air-fuel ratio becomes the target value. It is characterized by having a control procedure for switching between.

  (6) The control device includes a control procedure for adding an appropriate amount of high-calorie gas to low-calorie gas when the air-fuel ratio is insufficient to stably drive the gas engine during operation of the gas engine using low-calorie gas alone. It is characterized by that.

  (7) The control procedure is characterized in that a gas supply amount is controlled by setting a target value of the air-fuel ratio to a theoretical air-fuel ratio.

  (8) The control procedure is characterized in that the gas supply amount is controlled by setting the target value of the air-fuel ratio to a value that is richer than the value of the theoretical air-fuel ratio.

  As described above, according to the present invention, when the target value of the air-fuel ratio of the gas engine is set and the high-calorie gas and low-calorie gas supplied to the gas engine are switched, the air-fuel ratio becomes the target value. In addition, since the fuel is switched while controlling the supply amounts of both gases, stable switching can be performed without misfire.

  Specifically, since the air-fuel ratio value within the range in which the gas engine can be driven is set as the target value, and the opening of each gas supply valve is automatically controlled based on the target value, switching is performed. Stable switching can be achieved by increasing or decreasing the amount of two different calories while flexibly following changes.

  In addition, if the theoretical air-fuel ratio at which the fuel reacts in the engine without excess or deficiency is used as an index, the gas can be switched while using each gas efficiently. However, it is convenient for switching biomass gas, which is limited, and can save consumption of high-calorie gas, so that the energy efficiency of the entire system can be improved.

  In addition, the present invention provides an appropriate amount of high calorie gas to low calorie gas when the air-fuel ratio cannot maintain a value necessary for stable driving of the gas engine due to insufficient generation of biogas during steady operation of the gas engine. Since it is added, stabilization during steady operation can be achieved.

  FIG. 1 is a configuration diagram of a fuel switching device showing an embodiment of the present invention. The gas engine 1 drives the generator 2 by its operation and supplies electric power from the generator 2 to the electric load. Further, the exhaust gas of the gas engine 1 is used as a heat source for a hot water supply facility or the like.

  As fuel gas of the gas engine 1, a low calorie gas (for example, biogas) and a high calorie gas (for example, LPG, city gas) are supplied. These gas supply paths are provided with shut-off valves 3A and 3B and flow rate control valves 4A and 4B in series, respectively, so that the respective gas shut-off and flow rate can be adjusted.

  These flow-adjusted high calorie gas or low calorie gas is mixed with air in the mixer 5 and supplied to the gas engine 1. The amount of supply air is adjusted by the flow rate control valve 6, and the mixing ratio with the high calorie gas or the low calorie gas is adjusted.

  The control device 7 is functionally configured by computer resources and software using the computer resource. The oxygen sensor 8 provided in the exhaust part of the gas engine 1 is an air-fuel ratio sensor, the speed sensor 9 is an engine speed sensor, and the air-fuel ratio is calculated. Based on this, the opening / closing control of the shut-off valves 3A, 3B and the flow rate control of the flow rate adjusting valves 4A, 4B, 6 are performed.

  Biogas is made from wood chips that are gasified in a gasification furnace (not shown). The main combustion component of this gas is carbon monoxide, and the second component is methane and hydrogen. Existing. The biogas generated in the gasification furnace is once stored in the gas holder and then supplied to the gas engine. The calorie of the gas is 1600-2200 kcal / m3N during normal operation.

  FIG. 2 shows an example of a gas switching control flow when the gas engine is started by the control device 7 in the above apparatus configuration. First, the high calorie gas (LPG) and air flow control valves 4A and 6 are opened to the initial opening (S1), and the shutoff valve 3A provided in the high calorie gas (LPG) flow path is opened (S2). Then, the engine is started by LPG alone, and the engine speed is made to coincide with the set speed (S3, S4).

  At this time, since the value of the air-fuel ratio is known by the oxygen sensor 8, the value of the theoretical air-fuel ratio (14.5 in this case) that the fuel reacts without excess or deficiency is set as the target value, and this target value is set. The opening degree of the flow control valve of the LPG flow path is adjusted, for example, in units of 0.1% (S5, S5A). The optimum opening at this time can be set to open at that opening from the beginning if known in advance.

  When the value of the air-fuel ratio reaches the target value, the biogas channel shutoff valve 3B is opened (S6), and the biogas flow control valve 4B is opened by a predetermined amount. When the biogas valve is opened, the air-fuel ratio is shifted to the rich side, and the LPG flow control valve is closed by a predetermined amount so as to return to the target value (S7 to S11). For example, if the biogas flow control valve is set to be opened by 0.5%, the opening degree of the LPG flow control valve 4A is set to a predetermined amount (for example, for an air-fuel ratio that becomes rich when the biogas flow control valve is opened by 0.5%). 0.1%) The operation of changing the closing direction is performed by feedback control until the target value is returned, and when the target value is reached, the biogas flow rate control valve 4B is opened by 0.5%.

  The above operation is repeated until the LPG flow control valve 4A is fully closed (S10). After the gas switching operation is completed, the control of the biogas flow control valve 4B is shifted to the steady operation as control for maintaining the target value of the air-fuel ratio (S12 to S14).

  In the starting control up to this point, the target value of the air / fuel ratio is set to the value of the theoretical air / fuel ratio at which the fuel reacts without excess or deficiency, but the low-calorie biogas is input when its properties change suddenly due to disturbance. There is a possibility that the gas may become lean at once and misfire. In order to avoid this, it is preferable that the switching is set so that it is richer than the theoretical air-fuel ratio (for example, the air-fuel ratio is 13.0 to 14.5), so that there is a margin. . However, if it is too close to the stoichiometric air-fuel ratio, it is meaningless as a buffer, and if it is too rich, gas utilization efficiency may deteriorate or misfire may occur due to lack of oxygen.

FIG. 2 shows an example of the gas switching control flow at the time of starting the gas engine. The gas flow rate adjustment based on the air-fuel ratio in the gas switching control is executed during the steady operation of the gas engine, so that Can be stabilized.
In this control, if the air / fuel ratio is not sufficient to stably drive the gas engine due to insufficient gas generation during steady operation of the gas engine, the calorie is insufficient by adding an appropriate amount of high calorie gas to the low calorie gas. To ensure stable operation without causing misfire in the gas engine.

  1 shows a case where the opening / closing control of the high-calorie gas flow control valve 4A and the low-calorie gas flow control valve 4B is performed separately, but the flow control valves 4A and 4B are controlled simultaneously. The same operation and effect can be obtained by controlling the operation. For example, in conjunction with performing control to close the flow rate control valve 4A at a constant speed, control is performed to open the flow rate control valve 4B while changing the speed according to the air-fuel ratio.

The block diagram of the fuel switching device which shows embodiment of this invention. Control flow of the control device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Gas engine 2 Generator 3A, 3B Shut-off valve 4A, 4B Flow control valve 5 Mixer 6 Flow control valve 7 Controller

Claims (8)

A fuel switching device for a gas engine that shifts a gas engine driven with high calorie gas to operation with a single supply of low calorie gas,
A high calorie gas valve capable of shutting off and adjusting the flow rate of the high calorie gas supplied to the gas engine;
A low calorie gas valve capable of shutting off and adjusting the flow rate of the low calorie gas supplied to the gas engine;
A control device capable of blocking the valve and adjusting the flow rate;
The control device sets the target value of the air-fuel ratio of the gas engine, and switches the fuel of the gas engine while controlling the supply amount of the high calorie gas and the low calorie gas so that the air-fuel ratio becomes the target value. A gas engine fuel switching device characterized by comprising control means for switching between the two.   The control device includes control means for adding an appropriate amount of high-calorie gas to low-calorie gas when the air-fuel ratio becomes insufficient to stably drive the gas engine during operation of the gas engine using low-calorie gas alone. The fuel switching device for a gas engine according to claim 1.   The fuel switching device for a gas engine according to claim 1 or 2, wherein the control means controls the gas supply amount by setting the target value of the air-fuel ratio to a theoretical air-fuel ratio.   The fuel for a gas engine according to claim 1 or 2, wherein the control means controls the gas supply amount by setting the target value of the air-fuel ratio to a value that is richer than the value of the stoichiometric air-fuel ratio. Switching device. A gas engine fuel switching method for shifting a gas engine driven with high calorie gas to operation with a single supply of low calorie gas,
A high calorie gas valve capable of shutting off and adjusting the flow rate of the high calorie gas supplied to the gas engine;
A low calorie gas valve capable of shutting off and adjusting the flow rate of the low calorie gas supplied to the gas engine;
A control device capable of blocking the valve and adjusting the flow rate;
The control device sets the target value of the air-fuel ratio of the gas engine, and switches the fuel of the gas engine while controlling the supply amount of the high calorie gas and the low calorie gas so that the air-fuel ratio becomes the target value. A fuel engine fuel switching method characterized by comprising a control procedure for switching between the two.   The control device comprises a control procedure for adding an appropriate amount of high calorie gas to low calorie gas when the air fuel ratio becomes insufficient to stably drive the gas engine during operation of the gas engine with low calorie gas alone. The fuel switching method for a gas engine according to claim 5.   7. The fuel switching method for a gas engine according to claim 5, wherein the control procedure sets a target value of the air-fuel ratio to a stoichiometric air-fuel ratio to control a gas supply amount.   7. The fuel for a gas engine according to claim 5, wherein the control procedure sets the target value of the air-fuel ratio to a value that is richer than the value of the theoretical air-fuel ratio and controls the gas supply amount. Switching method.

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