JP2005106561A - Gas leak detection system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gas leak detection system for detecting a gas leak without using a gas detector. <P>SOLUTION: Occurrence of a gas leak is detected indirectly by grasping various state changes (a gas flow rate, a vapor pressure, a vapor temperature, a drain quantity) resulting from the gas leak to the inside (shell inside) of a gas heater. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a gas leak detection system in a cylinder in a gas heater using steam as a heat source.

  Gas heaters use various fluids such as steam, hot water, and combustion gas as heat sources in various fields, and have various shapes. Shell-and-tube heat exchangers as gas heaters are separated on the gas side and steam side (inside the cylinder) with the tube plate as the boundary, but the tubes in which gas flows in the cylinder are damaged by corrosion, etc. When leakage occurs, the pressure on the gas side is higher than the vapor pressure on the inside of the cylinder, so that a pressure difference occurs and gas is mixed into the cylinder. As a result, there is a risk that the gas diffuses not only in the trunk but also to the drain pipe connected to the trunk. In plants that handle gas heaters, the gas in the gas heater body is sampled from the safety standpoint, and when the gas reaches a certain concentration or higher, an alarm is issued and the gas leak is reported to the operator. There are many needs for detection systems.

  However, with this technique, there are problems in the detection accuracy due to the heat resistance and condensation of the gas detection element, and gas sampling containing water vapor is very difficult. Therefore, at present, a method is adopted in which the sampled gas is sent to a vapor separator or the like, and the temperature is lowered to a temperature and humidity condition where the gas detection element can be used, and then the gas detector detects the gas.

As a gas detection system equipped with a conventional steam separator, for example, JP-A-2002
There is a technique described in Japanese Patent No. 90270. A hollow fiber membrane or the like is used as a means for separating the vapor. As a technique for detecting minute gas leakage using a gas pressure and temperature sensor, there is one disclosed in JP-A-2002-323398. In this prior art, gas leak detection to the outside while the apparatus is stopped is targeted, and by measuring the internal pressure drop in a sealed state after a certain period of time has elapsed since the gas inflow was shut off, The presence or absence of external leakage is detected.

JP 2002-90270 A

JP 2002-323398 A

  As described above, by using a steam separator or the like, gas leakage in the gas heater body can be detected. However, steam separators and the like are generally expensive because they are less versatile and need to be designed according to the operating pressure and temperature conditions. The steam separator described above uses cooling water and instrument air to remove water vapor, and there is still room for improvement in terms of economy and environment.

  The objective of this invention is providing the gas leak detection system which detects a gas leak indirectly, without using a gas detector.

  The present invention indirectly detects the presence or absence of gas leakage by capturing various state changes (gas flow rate, vapor pressure, vapor temperature, drain amount) associated with gas leakage into the gas heater (inside the cylinder). Is.

  According to the present invention, it is possible to indirectly detect gas leakage without using a gas detector.

  Gas heaters use various fluids such as steam, hot water, and combustion gas as heat sources in various fields, and have various shapes. In the gas detection system of the present embodiment, the heat source fluid is superheated steam, and the heated fluid is a high-pressure gas such as natural gas. In order to simplify the description, the gas heater will be described with a typical example of a shell and tube heat exchanger having a general shape.

  Shell-and-tube heat exchangers are separated on the gas side and steam side (inside the cylinder) with the tube plate as the boundary, but the tube in which the gas flows in the cylinder is damaged due to corrosion, etc. and leakage occurs Since the pressure on the gas side is higher than the steam pressure inside the cylinder, a pressure difference is generated and gas is mixed into the cylinder. As a result, there is a risk that the gas diffuses not only in the trunk but also to the drain pipe connected to the trunk. In plants that handle gas heaters, the gas in the gas heater body is sampled from the safety standpoint, and when the gas reaches a certain concentration or higher, an alarm is issued and the gas leak is reported to the operator. There are many needs for detection systems.

  However, in the current technology, there is a problem in the detection accuracy due to heat resistance and dew condensation of the gas detection element, and gas sampling including water vapor is very difficult. Therefore, at present, a method is adopted in which the sampled gas is sent to a vapor separator or the like, and the temperature is lowered to a temperature and humidity condition where the gas detection element can be used, and then the gas detector detects the gas.

  FIG. 5 shows a conceptual diagram of a gas sampling method of a general gas heater.

  The gas heater 1 is separated into a gas side and a vapor side (body side) by a tube plate 2. On the steam side, pressure control is performed by the pressure transmitter 3 and the steam pressure control valve 4, and the tube 5 in the body is heated with steam. On the other hand, the gas side enters from the inlet nozzle 6 and flows through the tube 5, whereby the cold gas is heated by the steam and flows to the outlet nozzle 7. Further, since the steam in the cylinder is subjected to heat exchange in the tube 5, it is liquefied and discharged from the drain nozzle 8 as water.

Since the vapor pressure in the cylinder is lower than the gas pressure, when leakage occurs in the tube or the like, the gas is diffused in the cylinder. Since it is very difficult to directly detect the gas containing water vapor as described above, it is detected by the gas sensor unit 10 after the water vapor is removed by the vapor separator 9. The steam separator 9 removes water vapor using cooling water or dry instrument air. The removed water vapor is liquefied and drained from the vapor separator 9. The gas sensor unit 10 is a system that issues an alarm and notifies an operator when a gas concentration of a specified value or more is detected. In general, the steam separator 9 is provided with an orifice 11 at the front stage of the steam separator 9 from the viewpoint of economy to minimize the sampling amount and reduce cooling water and instrument air.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a first embodiment of the present invention.

  The gas heater 1 is separated into a gas side and a steam side (inside the trunk) by a tube plate 2. The steam in the trunk is pressure-controlled by a control pressure transmitter 3 and a steam pressure control valve 4 installed in the trunk. The steam (heated fluid) in the cylinder exchanges heat with the cold gas (heated fluid) flowing through the tube 5 and is liquefied and discharged as water (drain) when cooled.

  If the heat exchange of the gas heater 1 is normally performed, the gas flow rate and the steam flow rate are in a proportional relationship. However, when gas leaks into the cylinder due to tube leak, etc., the pressure in the cylinder rises slowly or suddenly depending on the degree of tube damage, but on the other hand, the steam pressure that controls the pressure in the cylinder The valve opening of the control valve is controlled in the closing direction to reduce the pressure, and becomes uncontrollable when the valve is fully closed. As a result, an event occurs in which the steam pressure control valve 4 is fully closed despite the gas leaking into the gas heater 1 (heating fluid side region), and the gas flow rate at which heat exchange is normally performed. There is an event that clearly differs from the relationship between the valve opening degree of the steam pressure control valve 4.

  Using this characteristic, the gas flow rate and the valve opening degree of the steam pressure control valve 4 are monitored to detect gas leakage indirectly. Although it is possible to replace the steam flow rate with the steam flow rate instead of the steam pressure control valve 4, the present embodiment will be described by taking the steam pressure control valve 4 as an example.

The valve opening of the steam pressure control valve 4 is measured by a valve opening transmitter 21. On the other hand, the valve opening degree of the steam pressure control valve 4 during the planned operation is obtained by the flow rate transmitter 22 and the steam pressure control valve opening function generator 23 of the system for supplying the gas to be heated to the gas heater 1. That is, the steam pressure control valve opening function 23 calculates the valve opening of the steam pressure control valve 4 defined from the relationship with the gas flow rate as shown in the figure based on the gas flow rate detected by the flow rate transmitter 22. . Then, the difference between the valve opening during the planned operation and the valve opening actually measured by the valve opening transmitter 21 is obtained by the subtractor 24, and the deviation more than the specified value (α% opening or more) is detected by the comparator 25. If it is recognized, a gas leak is judged and an alarm is issued.

  In addition, the gas heater 1 in which the gas temperature and the gas pressure are changed is assumed to measure the accurate flow rate by performing the temperature pressure correction on the gas flow rate. Further, when the gas heater 1 is started, the steam pressure control in the cylinder is unstable, and the valve opening degree of the steam pressure control valve 4 is not stable, so that an alarm is issued so as not to generate an inadvertent alarm. By providing an AND circuit 28 with a signal 26 during operation of the gas heater and a timer 27 as a condition, an alarm at the time of activation is excluded. In addition, by installing the gas shutoff valve 29 of the gas supply system and the steam shutoff valve 30 of the steam supply system, when a gas leak is detected, a gas leak detection system that can automatically shut off the gas and steam supply is provided. You can also.

  FIG. 2 shows another embodiment of the present invention. In the embodiment of FIG. 1, gas leakage was detected from the relationship between the gas flow rate and the valve opening of the steam pressure control valve 4, but in this embodiment, saturated steam was determined from the measured value of the steam pressure in the body of the gas heater 1. This is a technique for calculating a saturated steam temperature based on a pressure-temperature function and monitoring a deviation from the measured value of the steam temperature to detect a gas leak.

  If heat exchange is performed normally, the steam pressure temperature in the cylinder is almost saturated. Here, when a gas leak occurs in the cylinder due to a tube leak or the like, the pressure in the cylinder rises. The steam pressure control valve 4 is controlled in the closing direction so as to reduce the pressure, and becomes uncontrollable when the steam pressure is fully closed. As a result, the inflow of steam, which is a heat source, is blocked, and the temperature in the cylinder is lowered. Although the pressure in the cylinder is increasing, an event occurs in which the temperature in the cylinder decreases, and an event that is clearly different from the relationship of normal saturated steam pressure temperature occurs. In this embodiment, instead of the temperature deviation at the saturated steam pressure temperature, it can be replaced by a pressure deviation, but here, the temperature deviation will be described as an example.

  A flow rate transmitter 31 is provided for monitoring the temperature in the cylinder, and the steam temperature in the cylinder during planned operation is obtained by a pressure transmitter 32 and a saturated steam pressure temperature function generator 33. Specifically, the steam pressure inside the saturated gas heater 1 is detected, and a saturated steam pressure temperature function generator 33 in which the saturated steam pressure and the saturated steam temperature are in a proportional relationship as shown in the figure. Based on the above, the saturated steam temperature is calculated. Then, a subtractor 34 obtains a deviation between the steam temperature during the planned operation and the steam temperature actually measured by the flow rate transmitter 31. If the comparator 35 shows a deviation greater than the specified value (α ° C. or more), it is determined that the gas has leaked and an alarm is issued.

Note that when the gas heater is started, the steam pressure in the cylinder is unstable, and an AND of the signal 36 during operation of the gas heater and the timer 37 is set as a condition for generating an alarm so as not to generate an inadvertent alarm. By providing the circuit 38, an alarm at the time of activation is excluded. In addition, when a gas leak is detected, a gas leak detection system that can automatically shut off the gas and vapor supply by installing the gas shut-off valve 29 and the steam shut-off valve 30 can be provided.

  FIG. 3 shows another embodiment of the present invention. When the gas heater is operating normally, the flow rates at the gas inlet and outlet are the same. However, when a gas leak occurs due to a tube leak or the like, the gas also flows out into the trunk and the drain pipe connected to the trunk, resulting in a large flow deviation. In this embodiment, gas leakage is detected from the deviation between the gas flow rate flowing into the gas heater 1 and the gas flow rate flowing out from the gas heater 1. It is also possible to replace with a pressure deviation (differential pressure) instead of a flow rate deviation.

  The gas flow rate at the inlet / outlet of the gas heater 1 is measured by the flow rate transmitter 41 on the inlet side and the gas flow rate transmitter 42 on the outlet side. A deviation is obtained from the actually measured gas flow rate by the subtractor 43. If a deviation greater than a predetermined value (αkg / h) is recognized by the comparator 44, it is determined that the gas leaks and an alarm is issued.

  On the other hand, even when gas leaks to the outside (in the atmosphere), the flow rate deviation becomes large, so a diffusion type gas detector is installed near the gas heater, and leakage to the outside is also monitored at the same time. The gas outlet flow rate increases in pressure loss and temperature because it passes through the tube in the gas heater, but the inlet flow rate also requires an accurate flow rate deviation, so the inlet / outlet gas flow rate is corrected for temperature and pressure. . In addition, when a gas leak is detected, a gas leak detection system that can automatically shut off the gas and vapor supply by installing the gas shut-off valve 29 and the steam shut-off valve 30 can be provided.

  FIG. 4 shows another embodiment of the present invention. In this embodiment, the flow rate of gas supplied to the gas heater 1 is detected, the drain amount is calculated based on the drain generation amount function, and the deviation between this and the measured drain amount is monitored to detect gas leakage. To do.

  When the gas heater is operating normally, the gas flow rate and the amount of steam drain (water) in the cylinder are in a proportional relationship. When a gas leak such as a tube leak occurs, the pressure in the cylinder rises, but the steam pressure control valve is controlled in the closing direction to reduce the pressure, and becomes uncontrollable when the valve is fully closed. As a result, since the inflow of steam, which is a heat source, is blocked, the heat exchange performance is degraded. Despite the gas flowing, an event occurs in which the vapor drain amount decreases.

  Since the steam drain amount is proportional to the gas flow rate, the flow rate transmitter 31 measures the gas flow rate. The measured gas flow rate and drain generation amount function generator 51 obtains the drain generation amount during the planned operation. The subtractor 53 obtains a deviation between the drain flow during the planned operation and the actually measured drain flow by the flow transmitter 52, and when a deviation (αkg / h or more) exceeding a specified value is recognized by the comparator 54, the gas Judge as a leak and issue an alarm.

  In addition, the gas heater 1 in which the gas temperature and the gas pressure change is assumed to perform a temperature-pressure correction on the gas flow rate and measure an accurate flow rate. In addition, since the amount of drain generated in the cylinder is unstable when the gas heater is started, an AND circuit 28 with the signal 26 during operation of the gas heater and the timer 27 is provided as a condition for issuing an alarm. Exclude alarms. In addition, when a gas leak is detected, a gas leak detection system that can automatically shut off the gas and vapor supply by installing the gas shut-off valve 29 and the steam shut-off valve 30 can be provided.

  As described above, the gas leak detection system of the present embodiment shown in FIGS. 1 to 4 can detect gas leak indirectly without using a gas detector. This eliminates the need to install a steam separator and the like, and can reduce installation space, installation cost, utilities such as cooling water and instrument air used for the steam separator, and has great economic and environmental advantages. In addition, according to the standards related to general high-pressure gas safety regulations, gas detector maintenance inspections are required to be inspected at least once a year, and maintenance inspection costs are incurred over the long term. Since it is not necessary to use a gas detector, the maintenance cost of the gas detector is not required.

The conceptual diagram of the gas detection system which is one Example of this invention. The conceptual diagram of the gas detection system which shows the other Example of this invention. The conceptual diagram of the gas detection system which shows the other Example of this invention. The conceptual diagram of the gas detection system which shows the other Example of this invention. The conceptual diagram of the gas sampling method of a general gas heater.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Gas heater, 2 ... Tube plate, 3 ... Pressure transmitter, 4 ... Steam pressure control valve, 5 ... Tube, 6 ... Gas inlet nozzle, 7 ... Gas outlet nozzle, 8 ... Drain nozzle, 9 ... Steam separator, DESCRIPTION OF SYMBOLS 10 ... Gas sensor part, 11 ... Orifice, 21 ... Valve opening transmitter, 22, 41, 42, 52 ... Flow transmitter, 23 ... Steam pressure control valve opening function generator, 24, 34, 43, 53 ... Subtractor 25, 35, 44, 54 ... Comparator 26 ... Signal during operation of gas heater 27 ... Timer 28 ...
AND circuit, 29 ... gas cutoff valve, 30 ... steam cutoff valve, 31 ... flow rate transmitter, 32 ... pressure transmitter, 33 ... saturated steam pressure temperature function generator, 51 ... drain generation amount function generator.

Claims (4)

  In a gas detection system of a gas heater using steam as a heat source, a predetermined relationship exists between a flow rate of gas supplied to the gas heater and a valve opening degree of a steam pressure control valve that adjusts the steam pressure supplied to the gas heater. Based on the function generator set to, calculate the valve opening of the steam pressure control valve from the detected value of the flow rate of the gas supplied to the gas heater, and the calculated valve opening and the actual steam pressure control valve A gas leakage detection system that detects gas leakage when a deviation occurs in the valve opening of the valve.   In the gas detection system of the gas heater using steam as a heat source, the steam in the gas heater is based on a function generator in which the saturated steam pressure and the saturated steam temperature in the gas heater cylinder are set in a predetermined relationship. A gas leak detection system characterized by calculating a steam temperature from a detected pressure value and detecting a gas leak when a deviation occurs between the calculated steam temperature and an actual detected steam temperature value.   In a gas detection system of a gas heater that uses steam as a heat source, a gas leak is detected when a deviation occurs between a detected value of a flow rate of the steam supplied to the gas heater and a detected value of the flow rate of the steam discharged from the gas heater. A gas leakage detection system characterized by that. In the gas detection system of a gas heater using steam as a heat source, gas heating is performed based on a function generator in which a flow rate of gas supplied to the gas heater and a drain flow rate of the gas heater are set in a predetermined relationship. A gas leak detection system characterized in that a drain flow rate is calculated from a detected value of a gas flow rate supplied to a vessel, and a gas leak is detected when a deviation occurs between the calculated drain flow rate and an actual drain flow rate. .

Images