MXPA00004605A - Sample retrieval system - Google Patents

Abstract

A method and apparatus for collecting fugitive emissions from valves and other emissions sources (12) is disclosed. The apparatus comprises a capsule (102) enclosing at least a portion of the equipment and an ejector (140) in fluid flow communication with the capsule (102). The ejector (140) is connected to a compressed air source (30), which creates a pressure drop in the ejector (140) which draws emissions from the capsule (102) into the ejector (140). The apparatus may include a sensor chamber (114) housing gas sensors (200) to detect the presence and concentration of any emissions from the equipment being monitored, and may store emissions data, communicate the data to a plant process control system, and use the data to control plant conditions to reduce or eliminate the emissions.

Description

SYSTEM OF RECOVERY OF SAMPLES BACKGROUND OF THE INVENTION A. FIELD OF THE INVENTION The present invention relates in general to systems for collecting fluid samples and, more particularly, to an apparatus and method for collecting fugitive emissions from process equipment. B. DESCRIPTION OF THE RELATED TECHNIQUE Industrial plants that handle volatile organic compounds (VOCs) typically experience unwanted emissions of these compounds in the atmosphere from point sources such as chimneys and non-point sources such as valves, pumps, and installed settings. in tubes and vessels containing volatile organic compounds. Non-point source emissions, called "fugitive" emissions, typically occur due to leakage of volatile organic compounds from seals and seals. Fugitive emissions from control valves can occur as leaks through the gaskets between the valve stem and the valve body. Valves used that in demanding service conditions involving frequent movement of the valve stem and large temperature fluctuations typically experience an accelerated deterioration of the valve stem packing, resulting in higher fugitive emissions than those of the valves in service less applicant. Although improvements in the materials and design of valve stem seals have reduced fugitive emissions and lengthened valve seal life, monitoring of fugitive emissions has become important as a means to identify and reduce fugitive emissions and comply with the strictest emissions regulations. The Environmental Protection Agency (EPA) has enacted regulations that specify the maximum allowable leakage of certain hazardous air pollutants from control valves, and that require periodic monitoring of emissions from control valves. Current methods for monitoring fugitive emissions involve manual procedures using a portable organic vapor analyzer. This manual method is time consuming and expensive to carry out, and it also produces inaccurate results due to the ineffective collection of fugitive emissions from the equipment being monitored. If measurements are made on a valve exposed to the wind, valve emissions can be dissipated before the vapor analyzer can adequately measure the concentration of the emissions. Also, if the analyzer does not move carefully around the valve to capture all the emissions from the valve, it will result in an inaccurate measurement. Manual measurement methods also require plant personnel to spend a significant amount of time doing the measurements, distracting them from other tasks. Automated monitoring and detection of fugitive emissions can produce significant advantages over existing manual methods. The regulations of the Environmental Protection Agency require supervision of fugitive emissions at regular intervals. The periodicity of the supervision interval can be monthly, quarterly, semi-annually or annually; the required supervision becomes less frequent if the operator of the facilities can document a percentage lower than a certain percentage of control valves with excessive leakage. In this way, achieving a low percentage of leaking valves reduces the number of supervisions required per year. In large industrial facilities where the total number of monitoring points can vary from 50,000 to 200,000 points, this can result in great cost savings. Installing automated fugitive emission capture systems in valves subject to the most demanding service conditions and thus most likely to develop leaks, compliance with the regulations of the Environmental Protection Agency for complete installations is more easily achieved. This results in longer intervals between the supervisions for all the valves, significantly reducing the time and expense of manually taking measurements of the valves without automated feedback systems. Early detection of fugitive emissions from leaky valves also allows repairs to be made more timely, reducing the amount of hazardous material emitted and reducing the cost of lost material. Accurate capture of fugitive emissions provides an early warning system that can alert the facility operator to a potential failure of a valve seal and allow preventive measures to be taken before an excessive leak occurs. However, using an automated fugitive emission sensing system in an industrial environment requires designing a sample recovery system that can efficiently collect fugitive emissions emanating from a piece of equipment and transport the emissions to gas sensors. The sample recovery system must be capable of supplying a stream of samples at a known flow rate in order to allow the gas sensors to make accurate and consistent measurements of the concentration of fugitive emissions. The sample recovery system must be inexpensive to manufacture, and use an energy source that is readily available in typical process plants, in order to keep installation costs to a minimum. The system should be suitable for use in hazardous areas subject to an explosion risk, requiring the electrical equipment to be intrinsically safe or explosion-proof. It must also be able to operate in harsh environments, including areas subject to hose cleaning, high humidity, high and low temperatures, and vibration. The system must also be simple and reliable, in order to keep maintenance costs at a minimum. In accordance with the foregoing, it is an object of the present invention to provide an apparatus and method for automatically collecting emissions from equipment that is convenient for industrial applications. Another object of the present invention is to provide an apparatus and method that provides an accurate and consistent collection of fugitive emissions. Another object of the present invention is to provide an apparatus for collecting emissions that operates safely in hazardous environments. Another object of the present invention is to provide an apparatus and method for collecting emissions that uses an existing pneumatic energy source to collect the emissions. Still another object of the present invention is to provide an apparatus whose installation is simple and inexpensive. Another object of the present invention is to provide an apparatus and method for collecting emissions that provides little maintenance operation. Another object of the present invention is to provide an apparatus and method for collecting emission data and storing the data for later retrieval. Another object of the present invention is to provide an apparatus and method for collecting emission data and communicating this data to a remote plant process control system. Still another object of the present invention is to provide an apparatus and method for collecting emission data and using this data to control the plant to reduce or eliminate emissions. Still another object of the present invention is to provide an apparatus and method for collecting emission data and communicating this data to a remote plant process control system to enable control of the plant to reduce or eliminate emissions.

SUMMARY OF THE INVENTION According to one aspect of the invention, an apparatus for collecting emissions of equipment is provided wherein the apparatus includes a bonnet capsule (cap) that encloses at least a portion of the equipment. The apparatus also includes an ejector in fluid flow communication with the bonnet capsule. A source of pressurized fluid, which can be the air supply of instruments from the plant, is connected to the ejector, so that the flow of the pressurized fluid through the ejector creates a low pressure that extracts the emissions from the capsule. Bonnet towards the ejector. In accordance with another aspect of the invention, an apparatus is provided for collecting emissions from the equipment and storing the data for later retrieval. Loe datoe can be used to control plant conditions to reduce or eliminate emissions. The data can also be communicated to a separate process control system, which can control the conditions of the plant to reduce or eliminate emissions. According to another aspect of the invention, there is provided a method for collecting emissions from the equipment comprising enclosing at least a portion of the equipment within a housing, connecting an ejector in fluid flow communication with the housing; and supplying pressurized fluid to the ejector, thereby creating a low pressure in the ejector that acts to pull the emissions of the equipment towards the ejector.

BRIEF DESCRIPTION OF THE DRAWINGS The features and advantages of the present invention will be better appreciated after reference to the following detailed description and the accompanying drawings, in which: Figure 1 is a flow chart of an illustrative embodiment of the invention showing the most important components of a sample recovery system integrated into a fugitive emission sensing system. Figure 2 is a diagram of a seventh sample recovery according to the present invention. Figure 3 is a sectional view showing details of the bonnet capsule of the sample recovery system of Figure 2. Figure 4 is a sectional view showing details of the ejector of the sample recovery system of Figure 2 Although the invention is susceptible to various modifications and alternative forms, the specific embodiments have been shown by way of example in the drawings and will be described in detail herein. However, it should be understood that the invention is not intended to be limited to the particular forms described. Instead, the invention will cover all modifications, equivalents and alternatives that fall within the spirit and scope of the invention as defined by the appended claims.

DESCRIPTION OF ILLUSTRATIVE MODALITIES Turning now to the drawings and referring initially to Figure 1, a block diagram of an illustrative embodiment of the invention is shown which shows the most important components of a sample recovery system 100 integrated into a system fugitive emission sensor 10. A source of emissions 12 is shown, from which a sample stream 14 is pulled towards the sample recovery system 100. The sample stream 14 includes any emission (also known as the analyte) which emanates from the emission source 12. The sample recovery system 100 includes bonnet capsule 102, sensor chamber 114, and ejector 140. A gae sensor array 200 and a thermodynamic generator array 280 are located within the chamber of sensors 114. The sample stream 14 is pulled from the bonnet capsule 102 to the sensor chamber 114, exposing the sensor array of gas 200 and the thermodynamic sensor array 280 to the sample stream 14. The sample stream 14 then passes to the ejector 140. A source of compressed air 30 provides compressed air 32 to the ejector 140, creating a low pressure inside the ejector 140 which pulls the sample stream 14 through the sensor chamber 114 and towards the ejector 140. The compressed air 32 and the sample stream 14 are mixed within the ejector 140 and escape to the atmosphere as a mixture 36. The sample recovery system 100 is integrated with a remote calibration system 300, which is arranged to inject a small amount of the analyte that is being measured in the sample stream to allow automated calibration of the sample. the gas sensors. In addition, the control and communication system 400 is provided to process the outputs of the sensors and perform control and communication functions for the fugitive emission sensor system 10. The control and communication system 400 includes the sensor interface circuit 402, the microcontroller 404, the memory 406, the communication interface circuit 80, and a power conversion circuit 900. The gas sensor array 200 and the thermodynamic sensor array 280 are connected to the sensor interface circuit 402, the which processes the signals from the sensor arrays and provides the processed signals to the microcontroller 404. A convenient gas sensor and a sensor interface circuit is described in the United States of America patent application serial number: , (attorney's file number FEMR: 013) by John P. Dilger and Nile K. Dielschneider, entitled High Frequency Meaeuring Circuit, pre-filed concurrently with the preeente, whose designation is incorporated herein by reference. The microcontroller 404 stores data from the sensors in the memory 406, and can use sensor data received from the fugitive emission sensor device 10 to initiate control actions to reduce or eliminate the emissions. For example, the microcontroller 404 could close a valve upstream of the source of emissions 12 to stop the flow of fluid through the source of emissions 12 in order to stop the emissions caused by fluid leakage. Alternatively, the microcontroller 404 could alter the operation condition of the emission source 12 itself to reduce or eliminate the fugitive emissions. The microcontroller 404 can use the communication and control interface circuit 800 to provide these control signals to the upstream valve, the source of emisionese 12, or any other equipment in the plant that can be used to reduce or eliminate the emissions. The microcontroller 404 can also use the communication interface circuit 800 to provide sensor data to a process control system 40. The fugitive emission sensor system 10 can make measurements of fugitive emissions and immediately communicate the resulting sensor data to a system. of separate process control 40. Alternatively, the fugitive emulsion sensor system 10 can store sensor data of each measurement for subsequent retrieval by the process control system 40. The communication interface circuit 800 can also receive data. and controlling commands of the process control system 40. The process control system 40 can use the sensor data received from the fugitive emission sensing system 10 to initiate control actions to reduce or eliminate the emissions. For example, the process control system 40 could close an upstream valve or alter the operating condition of the source of emissions 12 as described above to reduce or eliminate fugitive emissions. The power conversion circuit 900 receives electrical energy, which can be transmitted over the communication link with the process control system 40, and provides power to the communication and control system 400 at a convenient voltage. The fugitive emission sensor system 10 can be used to detect the presence or measure the concentration of various types of fluid emitted from the emission source 12. The system can be used to detect hazardous substances., toxic, or pollutants emitted from the source, or to detect fugae de euetanciae no rieegoeae whose loss may be a cause for concern. The emissive fugitive sensor system can be used to detect emissions of any kind of origin, particularly induetrial process equipment from which they can spill risky euncianciae. Examples include control valves, block valves, or pumps installed in pipeline carrying risky gases; agitators, screw conveyors, or other equipment installed in process vessels containing risky fluids; and heat exchangers, reactors, and other process vessels containing fluid hazards. When the emissions are detected by the fugitive emission sensor system 10, these data can be used by the fugitive emission sensor system 10 to control the process so that emissions are reduced or eliminated. Alternatively, the data can be transmitted to a remote plant process control system 40 that can respond by controlling the process in a manner that reduces or eliminates emissions. Turning now to Figure 2, a diagram of a sample recovery system 100 is shown for use in the seventh fugitive emissivity sensor of Figure 1. The sample recovery system 100 comprises a bonnet shell 102, a manifold recovery 106, a sensor chamber 114, and the ejector 140. The bonnet capsule 102 is comprised of a die housing for enclosing the surface area of the source of emissions 12 from which an emission is anticipated. The manifold 106 is connected to one end of the bonnet capsule 102 and the other end to the sensor chamber 114, and allows a sample stream to flow from the emulsion source to the sensor chamber 114. The manifold 106 preferably is Build from 316 stainless steel pipe or other suitable corrosion resistant material.

The sensor chamber 114 contains the array of gas sensors 200, and may also contain a thermodynamic sensor array (not shown). The outlet 116 of the sensor chamber 114 is the inlet to the ejector 140. A pneumatic restriction was provided by a restriction orifice 118 at the inlet to the sensor chamber 114. The restriction orifice 118 induces a pressure drop in the chamber of sensors to assist the operation of the ejector 140. The restriction orifice 118 may be constructed of sapphire, stainless steel, or other suitable material that is inert to the expected emissions of the equipment being monitored. A particle filter 120 is located along the recovery manifold 106 to collect particles trapped in the sample stream. The flame path restrictors 124 and 126 are provided at an inlet to the sensor chamber 114 and at the outlet of the ejector 140. Microvalves 130, 132, and 134 are located in various positions to provide isolation of various parts of the system of sample recovery. The microvalve 130 can be used to isolate the bonnet capsule 102 from the sensor chamber 114. The microvalve 132 provides the ability to pull ambient air into the sensor chamber 114, allowing a baee line calibration to be performed on the sensor sensors. gas closing the micro valve 130 and opening the microvalves 132 A remote calibrator can be connected to the sample recovery system to allow the gas sensors to be calibrated without removing them from the sensor chamber 114. The remote calibrator 304 analyte cell containing Calibrator is connected through a first microvalve 306 to a dosing chamber 308. The dosing chamber 308 is connected through the second microvalve 310 to the sensor chamber 114. The sensor chamber 114 is preferably constructed of molded aluminum. The interior of the chamber can be left unfinished, or coated or machined to achieve a smooth finish to reduce surface sorption of gases from the sample stream. The sensor chamber 114 can be constructed of other suitable corrosion-resistant materials that are not affected by the emissions being monitored. The sensor chamber 114 is preferably constructed as a modular unit to allow replacement of the unit in the field. Turning now to Figure 3, a sectional view of the bonnet capsule of the sample recovery system 100 of Figure 2 is shown. The bonnet capsule 102 is shown mounted in an emission source 12, depicted in the drawing as a control valve. The bonnet capsule 102 includes an outlet 104 to which the recovery manifold 106 is connected, and may also include an opening 108 to allow the installation of the bonnet capsule 102 around a valve stem 220 or other obstruction parts of the valve. the source of emission. The arrangement of the bonnet cap 102 shown in Figure 2 is designed to collect gas leaks from the valve stem 16 gasket located between the valve body 18 and the valve stem 20. The aperture 108 is designed for have a small gap between the valve stem and the bonnet shell wall to limit the entry of foreign particles into the bonnet shell 102. A damper 110 is placed inside the bonnet shell 102 to restrict the entrance of the bonnet capsules. foreign particles in the bonnet capsule 102 to the recovery manifold 106. The bonnet capsule 102 is mounted in the source of emisionese so that a gap 112 remains between the bonnet blanket 102 and the emission source 12. This creates a restriction pneumatic low impedance, which allows air to flow through the gap 112, through the bonnet capsule 102, and into the recovery manifold 106. This air flow carries any issue fugitive emitted from the emission source to the recovery manifold 106 and to the sensor chamber. This continuous air flow also prevents fugitive emissions from the source of emissions 12 from accumulating in the bonnet shell. Eeta accumulation can result in a falsely high sensor reading due to the integration effect of an accumulation of fugitive emissions. The bonnet shell can be constructed of two or more pieces to facilitate installation in situations where the bonnet shell 102 should be installed around obstruction members. This is, a bonnet shell 102 as shown in Figure 3, comprising a housing divided vertically in two halves, can be installed around the valve stem 20 without removing a valve actuator mounted on the top of the valve stem (not shown). Bonnet cape 102 is preferably constructed of 316 stainless steel or other suitable corrosion resistant material. Figure 4 is a sectional view showing detail of the ejector 140 of the sample recovery system 100 of Figure 2. The ejector 140 can be integral to the sensor chamber 114 or can be constructed as a separate unit. A compressed air source 30 provides compressed air 32 to the microregulator 144 which provides regulated compressed air 34 to the ejector 140. The compressed air is used to provide the motive energy to extract the sample stream 14 from the bonnet case 102, through the sensor chamber 114, and towards the ejector 140. The source of compressed air 30 may be the su of instrument air typically used in processing plants to modulate the pneumatic control valves or operate pneumatic instruments, although other sources may be used of pressurized gas or pressurized liquid. The microregulator 144 is a small pressure regulator of a type commonly used in industrial acations. The microregulator 144 reduces and regulates the pressure of the compressed air to control the flow of the sample stream 14 and minimize the consumption of compressed air 32. A primary chamber 146 receives regulated compressed air 34 from the microregulator 144 and discharges air into a spout primary 148. Primary jet 148 is tubular in shape, with a hole 154 discharging toward throat of secondary jet 152. Secondary jet 150 is connected to manifold 106 and throat of secondary jet 152. Secondary jet 152 is shaped tubular, with a larger cross-sectional area than the primary jet 148, and an orifice 156 discharge to the atmosphere. In operation, the regulated compressed air 34 enters the primary chamber 146 and flows into the primary aerator 148. The regulated compressed air 34 increases in velocity as it enters the reeferred region at the outlet of the primary jet 148. This high velocity stream of compressed air discharges into the secondary jet 152, entraining air from the secondary chamber 150 and creating a low pressure in the secondary chamber 150. This pressure drop induces the flow of the sample stream 14 from the bonnet capsule 102, through of the recovery manifold 106, and to the secondary chamber 150. The sample stream 14 carries any fugitive emulsion from the emulsion source 12 to the sample recovery system, exposing the gas sensor array 200 and the thermodynamic sensor array 280 to the emissions. The regulated compressed air 34 and the sample stream 14 are mixed together in the secondary jet 152 and the mixture 36 escapes into the atmosphere. The ejector 140 can be made of stainless steel, or other corrosion resistant material. The primary orifice 154 and the secondary orifice 156 are preferably constructed of sapphire. The ejector 140 is designed to produce a known mass flow sample stream 14 through the sample recovery system 100. The expense of the sample stream 14 is determined by diameters of the primary orifice 154, the secondary orifice 156, the inlet of the sensor chamber 118, and the regulated compressed air pressure 34. The sample recovery system 100 operates satisfactorily at a sample current draw of approximately 1,203 liters per hour. This expense can be achieved with a primary orifice diameter of 0.279 millimeters, secondary orifice diameter of 0.588 millimeters, sensor chamber inlet diameter of 0.318 millimeters, and the regulated compressed air pressure of approximately 0.21 kilogram per square centimeter gauge. However, different dimensions and operating conditions for the ejector 140 may be required to effectively collect emissions from different types of emission sources. By controlling the pressure of the regulated compressed air 34 towards the ejector 140, the pressure drop inside the secondary chamber 150 can be controlled, and thus the speed of the sample stream 14 through the recovery manifold 106 and the sensor chamber 114 it can be controlled. In addition, the mass flow of the sample stream 14 can be calculated given the geometry of the ejector 140, the recovery manifold 106 and the sensor chamber 114, and the pressure of the compressed air at the inlet to the primary chamber 146. The design of the sample recovery system 100 thus eliminates the need for a mass flow sensor to measure the flow of sample stream through the recovery manifold 106. The described system also eliminates the need for pumps or fans located near of the emission source to collect the sample stream, resulting in a simple and inexpensive design. Finally, the sample recovery system can be designed to comply with the requirements for the collection of samples from the Environmental Protection Agency. Many modifications and variations can be made to the techniques and structures described and illustrated herein without departing from the spirit and scope of the present invention. In accordance with the foregoing, it should be understood that the methods and apparatus described herein are illustrative only and not limiting of the scope of the present invention.

Claims (13)

1. A system for collecting emission samples from a control valve (12) having a valve stem (20) the system comprising: a capsule (102) including an outlet (104), the capsule comprising a vertically divided housing in two halves to allow the installation of the capsule around the valve stem; a sensor chamber (114) having an inlet (118) and an outlet (116); a passage of fluid (106) that couples the entrance of the sensor chamber with the outlet of the capsule; and an ejector (140) coupled with the outlet (116) of the emanator chamber (114) and connectable to a source of pressurized fluid (30), so that the pressurized fluid flowing through the ejector creates a low pressure to induce the flow of a sample stream from the capsule, through the sensor chamber, and towards the ejector, by mixing the sample stream with the pressurized fluid in the ejector and being ejected therefrom. The system of claim 1 wherein the capsule (102) is adapted to form a low impedance restriction against the control valve. The system of claim 1 wherein the ejector (140) comprises a primary spout (154) and a secondary spout (156), the primary spout adapted to receive the pressurized fluid and discharge the pressurized fluid into the secondary spout. The apparatus of claim 3 further comprising a microregulator (144) for regulating the pressurized fluid pressure before the primary dispenser receives the pressurized fluid. The apparatus of claim 1 wherein the generator chamber (114) is integral with the ejector (140). The apparatus of claim 1 further comprising a source of calibration fluid in fluid flow communication with the sensor chamber (114). The system of claim 1 wherein the control valve (12) includes a valve stem packing (16) having an outer surface and wherein the capsule (102) circumferentially encloses the outer surface of the stem packing. valve of said valve. 8. The apparatus of claim 1 wherein the pressurized fluid comprises compressed air. The system of claim 1, further comprising: a communication and control system (400) connected to the sensor to generate indicator data of the concentration of the emisions extracted from the control valve. 10. The system of claim 9 further comprising a process control system (40) remotely connected to the communication and control system (400) to receive data and reduce emieions. The system of claim 10 wherein the communication and control seventh (400) comprises means for storing data (406) indicating the concentration of emissions from the control valve. The system of claim 11 wherein the communication and control system (400) comprises means for using the data (40) to reduce emissions. The system of claim 1 further comprising a cushion (110) located within the capsule (102) to restrict foreign particles from entering the fluid passage.