Patent Application
20150260397
The present disclosure relates to the monitoring and controlling of flaring operations in industrial plants.
A flare is a pressure safety relief device used to ensure that emergencies occurring in a plant (e.g., process upsets, compressor failures, etc.) do not compromise the safety and integrity of the plant. Such emergencies may require disposal of large volumes of hydrocarbons, and flaring is the best and practically the only option in these situations. Furthermore, at times, as part of a refining process, more fuel gas (e.g., propane, butane) is produced than needed by the plants. Flaring eliminates this excess process gas by burning it off rather than venting potentially damaging hydrocarbons to the atmosphere.
In industry today, as far as it is possible, flaring is avoided to prevent loss of valuable hydrocarbons as well as to minimize environmental damage. The flaring process introduces two major sources of pollution—smoke and noise. These two pollutants are strictly monitored by various environmental agencies, and there is an economical and societal need to reduce this significantly through improved monitoring and control.
In the following description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific embodiments which may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that structural, electrical, and optical changes may be made without departing from the scope of the present invention. The following description of example embodiments is, therefore, not to be taken in a limited sense, and the scope of the present invention is defined by the appended claims.
The present disclosure presents a comprehensive solution for monitoring and controlling flaring operations. A root cause analysis of various factors that necessitate flaring and the specific factors that cause extensive environmental damage is presented. An embodiment reduces the effects of the variables (or sub systems) that are responsible for flaring and pollution.
There are several issues that many industrial plants have to deal with today. One is the generation of heavy smoke during flaring operations. Because of this heavy smoke, many industrial plants are unable to meet strict environmental regulations. At least one cause of the heavy smoke is an ineffective smoke control system. Another issue is a lack of an automated monitoring solution for compressors, valves, etc. In an embodiment, compressors are monitored so as to prevent compressor failures, which will minimize flaring. Another issue is the lack of online gas composition estimation tools as part of the overall smoke control. In an embodiment, gas composition is monitored, and if the composition is detected as suboptimal (for good combustibility), an appropriate gas mixture is added. Another issue is the significant financial losses due to flaring and compressor problems.
In an embodiment, several modules can be integrated into a flare monitoring and control system. The system can include a monitoring module, relating to at least health monitoring and asset monitoring. The system can also include a machinery control system. The system can further include a field advisor that can monitor the performance of various process and equipment parameters.
In many industrial plants today, existing smoke control systems include steam injection. Such systems are automated, and the smoke detection is performed using infrared (IR) cameras. Some plants use air-assisted control. However, such control systems are not efficient for several reasons. One reason is that such systems do not take any inputs from other parts of the plant, for example, compressors, valves, etc. Also, for systems that use IR cameras, the control system takes input from the IR camera, which examines the flare (controller is tuned with a simple rule that large flares imply large smoke, and the converse), and releases an appropriate amount of steam. Such a control action is reactive in the sense that excess flaring or smoke is caused due to various processes/equipment behaving sub-optimally—and the smoke is the end result of complex failures in the plant or refinery. Also, the control system can react only after smoke detection. Consequently, there is a significant delay in control after the plant upsets, which usually renders control ineffective. Thus, there is a need for advanced monitoring techniques which can predict critical failures in industrial and refinery processes and equipment, and inform the control system of impending failures so that the control system can respond better.
Consequently, one or more goals of one or more embodiments include that the smoke that is generated during flaring should be reduced and/or eliminated, compressor reliability should be improved, and compressor tripping should be capable of prediction so that lag time (usually about thirty minutes to an hour) between the compressor tripping and a standby compressor starting should be reduced. Addressing the issues of compressor reliability and trip prediction will also help in reducing the smoke problem. Further, one or more embodiments include that the gas composition monitoring be made online and included in the overall smoke control loop.
A root cause analysis (with top-down approach) of smoke formation can be used to investigate the generation of smoke during flaring operations. The results of the root cause analysis can then be used to address the issues enumerated in the previous paragraph.
Referring to
There are several reasons the amount of flare gas could be large at 120. The large amount of flare gas could be the result of a valve failure as indicated at 123, or it could be the result of issues with a compressor at 125. The compressor issues at 125 could further be the result of compressor reliability issues at 127, which in turn could be the result of a shaft failure (127A), a bearing failure (127B), a compressor blade failure (127C), a surging failure (127D), a motor failure (127E), and/or a gear failure (127F). The compressor issues at 125 could also be the result of a time lag between a compressor tripping and the starting of a standby compressor, as indicated at 129. As illustrated at 129A, this lag time could be because a tripping prediction system is not in place. Additionally, as indicated at 129B, there may be no automatic way of starting the standby compressor when there is tripping. That is, the standby compressor must be manually started.
Regarding smoke creation from the gas composition at 130, the gas composition may not be monitored as indicated at 131, and the heating value of the gas could reduce combustion efficiency as indicated at 132. Both the gas composition and heating value of the gas can contribute to increased smoke during flaring.
Finally, the quantity and quality of the steam/air in an injection system could be insufficient. As illustrated at 142, the amount of steam or air that is provided may not be controlled in real time. Additionally, as indicated at 144, there may be reliability issues with an air compressor, a nozzle, or a valve.
The root cause analysis of
There are three typical flows to the flare system. First, there are emergency flows. Examples of an emergency flow include pressure relief flows and emergency depressurization. Second, there are episodic flows. Examples of episodic flows include venting that is required for maintenance, and venting that is required for regeneration and shutdown/startup operations. Third, there are continuous flows. Examples of continuous flow are a sweep gas that is put through the flare system piping, and pressure relief valve leakages. In any of these typical flows to the flare system, the amount of flare gas that is vented depends on the extent of valve failures, compressor failures, and/or process upsets. For example, if during normal conditions the flare gas flows at 4-6 million cubic feet per minute (mmcfm), and the compressor trips, the flare gas flow can increase to 150 mmcfm. This increase can cause excessive flaring and result in smoke and noise formation.
Compressor tripping can happen because of various individual component failures. When a compressor does trip, a standby compressor is started. Thereafter, it can take 30-60 minutes to reach steady state operating conditions. During this 30-60 minute period, the flaring can become very large.
When the flare gas is comprised of individual gases with high molecular weight, the smoke becomes thicker and black. However, when the flare gas is comprised of gases of lower molecular weight, the smoke becomes white and thinner. For example, ethylene (molecular weight-18 28) produces lighter smoke compared to butadiene (molecular weight˜54). Also, the gas composition changes the heating value of the gas, thereby affecting the combustion efficiency, resulting in higher levels of smoke creation. The steam quality with dryness factor and temperature can also affect the quality of the smoke.
The quantity and/or quality of steam or air plays an important role in the formation of the smoke. The failure of an air compressor or nozzle can cause excessive smoke formation.
An embodiment addresses the various factors that cause smoke and noise formation by integrating monitoring and control. In the monitoring part of the system, there are several parameters of interest. First, there is the reliability of the compressors. Compressor reliability is monitored by analyzing a compressor's vibration, noise, motor current, speed, performance parameters, etc. Second, there is the composition of the flare gas. There exist a few online techniques for detecting gas composition that are known to those of skill in the art. One technique uses an infrared (IR) sensor with appropriate filters for detecting spectral responses of various gases. In another embodiment, catalytic type combustible sensors are used. Laser gas detection systems are another option for gas sensing. Finally, solid state sensors can be used. Thus, there are a wide variety of options for online gas (composition) sensing in refineries and other industrial plants. Third, the monitoring involves monitoring steam quantity, steam quality, and air flow. Fourth, the monitoring involves flare and smoke monitoring. For smoke and/or flare detection, the two standard approaches include using an IR sensor and a normal charge-coupled device (CCD) sensor.
Based upon the data input into the monitoring system (210-222), and in particular, the amount of smoke or flaring (210), the various controlling parameters (251-258) are activated so as to control the smoke or flare. For example, if the pilot flame is visible (a blue color when LPG is used) during zero or low flaring, then the LPG flow rate (251) could be adjusted based on the requirement. Otherwise, the temperature of the pilot flame (211) (measured via thermocouples) can also be used for controlling the LPG flow rate. Similarly, if there is a large amount of smoke, then the steam/air quality (253, 254) and quantity (252) can be varied. The quality of air (253) can be controlled by providing an appropriate amount of oxygen or any other gas. The composition of the gas can also be varied using similar methods (258). The compressor control systems can be surge controlling, where the flow has to be varied using bleeding (256) or varying inlet guide vane (IGV) angle (255) or changing speed (257). Therefore, an embodiment using the integrated controls of
As further illustrated in
In summary, in the control system, the monitored variables described above (210-222) form the inputs to the control system. The control system executes the control of some compressor failure modes like surge, the control of the flare smoke and noise (using the air/steam control system (252, 253, 254)), and the control of steam/air quality (253, 254).
Referring to
At 330, the computer processor suggests preventative actions to eradicate or decrease the impending increase in the amount of smoke generated during the flaring operation. The computer processor may report to output device 280 that a liquid propane gas flow rate (212) is either too low or two high, which may decrease the efficiency of the plant, which in turn may increase the smoke generated during flaring.
At 335, the prediction of an impending increase in the amount of smoke generated during the flaring operation is based on an identification of a valve failure or a compressor problem. As indicated at 336, the identification of the compressor problem can include a shaft failure, a bearing failure, a blade failure, a surge failure, a motor failure, and/or a gear failure. Additionally, as indicated at 337, the compressor problem can include a time lag between the compressor problem and starting a standby compressor. In an embodiment, this lag time issue can be addressed by configuring a computer processor to cause a standby compressor to start immediately or substantially immediately after the identification of the compressor problem.
As indicated at 340, the flare monitoring and control system can monitor and control an industrial plant, and as indicated at 341, the industrial plant can be an oil or gas refinery or an oil or gas separation plant.
Block 345 indicates that the monitoring of the parameters includes monitoring a composition of a flare gas, and that a computer processor causes an injection of one or more gases into the flare gas to modify the composition of the flare gas.
Block 350 indicates that the monitoring of the parameters includes monitoring steam/air injection quantity and quality, and that a computer processor causes a modifying of the steam/air injection quantity.
Block 355 indicates that the monitoring of the parameters includes a monitoring of a flare image, a temperature at a liquid propane gas (LPG) discharge, a LPG flow rate, an air/steam injection rate, an air/steam quality, and/or a steam temperature, and that the computer processor causes a modifying of one or more of the LPG flow rate, the air/steam injection rate, and the air/steam quality as a function of the monitoring.
Block 360 indicates that the monitoring of the parameters includes a monitoring of a compressor. Specifically, the monitoring of the compressor includes the monitoring of one or more of vibration, noise, current, speed, radar signal, flow, discharge pressure, ambient pressure, discharge temperature, and ambient temperature. The computer processor causes the modifying of one or more of a compressor inlet guide vane (IGV) angle, a compressor bleeding, and a compressor motor speed or frequency as a function of the monitoring.
It should be understood that there exist implementations of other variations and modifications of the invention and its various aspects, as may be readily apparent, for example, to those of ordinary skill in the art, and that the invention is not limited by specific embodiments described herein. Features and embodiments described above may be combined with each other in different combinations. It is therefore contemplated to cover any and all modifications, variations, combinations or equivalents that fall within the scope of the present invention.
The Abstract is provided to comply with 37 C.F.R. §1.72(b) and will allow the reader to quickly ascertain the nature and gist of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.
In the foregoing description of the embodiments, various features are grouped together in a single embodiment for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting that the claimed embodiments have more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed embodiment. Thus the following claims are hereby incorporated into the Description of the Embodiments, with each claim standing on its own as a separate example embodiment.
