Equipment to Monitor and Control the Industry Gas Plant - Report Example

Equipment to monitor and control the industry gas plant Name Institution Date Equipment to monitor and control the industry gas plant Summary This paper discusses the various equipments used in industry to control the operation of the plants and to monitor performance against expected values. The paper first focuses on the process equipments by providing a discussion of the theory for each of the equipments before discussing its contribution the control of the industrial process. In this discussion, pumps, compressors and control valves were found to serve critical roles in the regulation of gas pressure, speed and direction. Also discussed were the instrumentation equipment. These were found to be greatly useful in the monitoring of industrial process. Through these equipments, it is possible to assess the condition of the whole plant by comparing the measured values of pressure, temperature, level and flow against expected values at different points in the plant. In this way, process controllers are able to detect any changes and identify parts of the plant that may have gotten damaged or worn out. As will be seen in the discussion, these equipments serve very important tasks in the plant and must always be healthy and functional. Introduction Industries are made up of several equipments that work in coordination in the production and processing of various materials and products. In the industry gas plant, for example, there are several equipments that are set up to achieve a dense network of operations that produce, monitor, control and transport the gas from the plant to the consumers. In these plants, it is critical to ensure that the plant is monitored and the process controlled effectively to avoid any losses and leakages that could arise given that most of the plants operate with very high gas pressures. This paper investigates some of the commonly used equipment in the gas industry. The paper discusses the theory behind the operation of each of the equipment and the contribution of the equipment to the control and monitoring of the industrial process, highlighting the importance of each in the industry Process equipments: Pumps A pump is equipment that is used to raise, transfer or compress fluids. These equipments convert mechanical energy into fluid energy and may be modeled using a system of affinity laws that represent relationships between flow rate, power and rpm. It is important to understand these basic relationships when considering the performance of any pumping system that is to be developed. These are shown below: Q1/Q2 = N1/N2 Q=Flow rate H1/H2 = (N1/N2)2 N=Speed P1/P2 = (N1/N2)3 H=Head, P=Power The basic types of pumps are the kinetic pumps and the positive displacement pumps. The most commonly used kinetic pumps are the centrifugal pumps. These pumps are commonly used in applications that require moderate to high flow with low head. These pumps are always more economical to operate and maintain as compared to other types of pumps. The process engineer will usually seek to specify the requirements of the process and the physical properties and conditions of the fluid as well as the flow rate, density, viscosity and pressure. The flow rate will determine the capacity of the pump, and the head will depend on the viscosity and density of the fluid. Generally, flow rate to be achieved will be determined by the balances between material and energy. Design margins, normally between 0-25%, are included in the material-balance flow rate to account for any variations in fluid properties or conditions so that the plant meets its performance criteria. The minimum flow protection is also included as continuous circulation The gas industry utilizes two major categories of pumps. The positive –displacement pumps work on the principle of isolation and subsequent compression of gas within a volume. The other category is the momentum transfer pumps which transfer gas molecules of a desired velocity direction and introducing an average shift towards the region with higher pressure (Hilleret, 2002). Several other classifications exist depending on the working principle, application, lubrication and several other factors. Fig: A lobe pump: working on the principle of positive displacement Pumps have been widely used to transport gas from one point to another within the plants. By controlling pumping speeds and operating time, processes controllers have been able to effectively regulate gas speeds within the facilities and achieved great control of the production processes. Pumps come in different speeds and have been selected depending on the system requirements of scale and speed of operation. Pumps have been linked to other devices like PLCs, sensors and other equipment to achieve great regulation of processes and automation in industry. By responding to signals from other parts of the operation, pumps have become one of the most important devices in the movement of gases and other fluids. Control valves Valves are used in pressure and fluid flow systems to regulate the pressure of the fluid or its flow. They may therefore stop and start fluid flow, control the flow rate, divert flow, prevent the back flow of fluids or relieve pressure. The control values are operated by adjusting the position of the closure member, which may be controlled either manually or automatically. Manually operated valves will include valve operation through the action of manually controlled power operator (Smith & Zappe, 2004). Valves may also be classified as globe valves and rotary valves. In a globe valve, the flow area is controlled by the position of the valve plug compared to its seat area. In a rotary valve, the other hand, the flow area depends upon the angular position of a notched sphere or disc within the passage area (Thomas, 1999). These have been illustrated below: Fig1: Schematic of a Fig2: Butterfly valve Fig: Steam conditioning valve global valve showing angle opening (angle style) Control valves can be used to stop and start gas flow, regulate the amount of fluid flow, control the direction of flow and even relieve the pressure within the component or pipes. Therefore, the devices are used to achieve a great amount of control in the gas industry by regulating the amount of gas through the valve. Complete closure of the valve means that the second part of the system is isolated and that the gas flow has either changed direction or has been stopped completely. In process circuits, these devices have become the most common elements that operate continuously to influence and control the processes in a specific manner. They connect and interface electronic control technology and the process medium. They also connect components between the phases of the process, thereby providing control to the continuous process flow by balancing out the pressure levels on different sides (Fliegen et al, 2007). Compressor Compressors have been manufactured for a variety of purposes and are of many types. Although they have been primarily designed to compress gas, many compressors are used as blowers or as vacuum pumps (Pirro & Wessol, 2001). Depending on the type of compressor and the gas being compressed, these devices require considerably varying lubrication requirements. Generally, though, air and gas compressors have several mechanical similarities. The major difference is the effect of the gas on the compressor components and the lubricant. Compressors may be classified into two: positive displacement or dynamic (Pirro & Wessol, 2001). Reciprocating (piston) types, diaphragm types, and several rotary types are referred to as positive displacement compressors. Dynamic compressors, on the other hand, could be axial flow type or centrifugal types, although machines with mixed flow that combine both elements have been developed. Centrifugal compressors have been extensively used in small gas turbines and are the units driven in most turbine compressor trains. They are widely preferred due to their smooth operation, higher reliability and tolerance of fluctuations in the processes. They range in size and application from pressure ratios of 1:3 per stage to as high as 12:1 on experimental models (Boyce, 2012). Gas processing requires several gas compressors that are designed for different stages of the processing. A gas gathering compressor and a sales compressor are shown below. These compressors are used to transport gas from the extraction source to the processing facility and from the facility to consumer centres respectively. The gas gathering compressors should be made of anti-corrosion materials due to the corrosive components like carbon dioxide and hydrogen sulphide found in gas from natural sources. The compression levels achieved will depend on transmission distances and the speed at which the gas should be transported. Fig: Gas collection compressor and Gas sales compressor, each with its drive motor Furnaces (boiler) A boiler is a device used to convert chemical energy in fuels into useful heat output in the form of steam or hot water. Different fuels have been used for boilers like gas, coal or oil. The burners burn this fuel and produce flames and combustion gases that transfer the heat to the incoming water. Boilers basically comprise of two systems. The steam water system or the waterside is where the water is introduced through water tubes and then converted to steam through heating. During such heating, it is important to ensure that the boiler maintains a chemical balance for it to operate properly. This may be achieved by ensuring a stable interaction with the feedwater control system. Blowdown must be controlled with reference to the feedwater particularly in cases where the blowdown is continuous. The boiler’s second system is the fuel air-flue gas system, also known as the fireside. This is the system that supplies the heat needed to heat the water. The inputs to the fireside are fuel and air. Within the furnace, there are three factors that must be controlled to achieve the desired results: time, turbulence and temperature. The control of the furnace draft is needed to ensure that a negative pressure is maintained in the furnace within balanced draft boilers (Gilman & Gilman, 2010). Boilers help in control majorly by regulating the amount of gas or steam that is released into the plant system. Boilers and furnaces are equipped with temperature sensors that relay the boiler temperatures in real time to controllers. When large amounts of water are fed to the boiler, and temperatures maintained at a high level, the system will likely experiences high pressures that will be noticed within the pipes and around the facility. To control these high pressures and excess steam production, the inputs to the boiler are regulated. The incoming water could be reduced and the temperatures maintained within levels that are sufficient to keep the steam produced within allowable levels. The boiler operation must therefore be maintained within levels that provide balance with the whole plant. The amount of steam or gas produced should be enough to maintain the system pressures so that other devices like control valves, pumps and transmitters operate effectively. Instrument devices: Flow transmitter Flow transmitters, also known as flow meters are used for measuring the flow of gas and other fluids in several fields. Several types of flow transmitters exist today. Selection of flow transmitters usually depend upon characteristics like flow profile, fluid characteristics, flow range and the degree of accuracy expected. Other factors for consideration like mechanical restriction and the output-connectivity options also influence the choice. When setting up such measurement systems, the effects of temperature, dynamic influences, pressure and the particular fluid must be taken into account. Industrial flow meters have been used in environments with significantly high noise levels and high voltages. To operate effectively, therefore, the analogue front end should operate at high common-mode voltages and must be able to have good noise performance and high sensitivity. Commonly used is the 4- to 20-mA loop to interface between the flow transmitters and the flow control equipment like PLCs. Flow transmitter can also operate on a dedicated power line (Kalyanaraman, 2012). Monitoring of the flow speeds is critical in gas plants. Information obtained from these transmitters gives the process controllers an idea about the whole operation. In an industrial plant, there are predetermined flow speeds expected at different points of the plant and the. Any differences in flow levels at these points are clear indication of problems or leakages in the plant. Breakages and chocking of gas pipes are likely to cause change of speeds which will be seen as speed variances in the flow transmitters. These variances when transmitted to monitoring centers, help inspectors to identify the exact locations of any such problems so that corrective maintenance is done in time. Temperature transmitter Temperature measurement is very important in industry. Several sensors have been developed to convert the heat into signals that can be measured. The simplest and most widely used method for sensing temperature has been the use of thermal expansion. For electric transduction, however, various methods have been employed. Some of these methods are thermoelectric, acoustic, resistive, semi conductive, piezoelectric and optical detectors (Faden, 2010). Once the heat energy from the source has been converted to an electrical signal, the signal is transferred and processed into readings that indicate the condition of the gas or steam. Industrial plants are designed to operate within specific temperatures and processes are regulated to remain within the allowable temperature ranges. Significant changes in temperature in gas industries may result to changes in pressure and flow speeds and thereby affect the operation of the whole system. It is therefore important to continuously monitor the temperatures and relay the results to a central monitoring point. Fig: Temperature transmitter – screw-in probe with Industrial Protection Head Pressure transmitter Pressure transmitters determine the pressure of gases and other fluids by using a variety of pressure sensors. Different types of pressure measurements also exist including gauge pressure, differential pressure and absolute pressure. Gauge pressure, for example, is measured with the atmospheric pressure serving as the reference. The piston type pressure gauge is one of the most accurate pressure measurement devices. In this device, the gas or vapour pressure acts on a piston that is enclosed within an oil filled pressure cell (Krishnamurthy, Vijayachitra & Krishnaswamy, 2005). To ensure that the pressure remains at a minimum, a small electric motor is used to rotate the piston continuously. The counterforce is provided by means of two helical springs. In this device, the piston is preloaded by weight to suppress the zero point and the reading displayed on a large-size dial. Through appropriate transducers, it is possible to feed the signal to other electrical indicators, control instruments or recorders by attaching these transducers to the movement of the piston. A piston-type pressure gauge and a panel mount transducer are shown below: Fig: piston type pressure gauge Fig: Panel Mount Transmitter Pressure transmitters provide information about the condition of the plant by showing any variances to the expected pressure values. Pressures higher than normal directly indicate system problems that could be as a result of overproduction of the gas, or blocked passages. Control valves and other devices for monitoring operate depending on the pressures in the pipes and tubes. Pressure information should therefore be accessed to inform the various processes that go on within an automated plant. Level transmitter Level transmitters are used for all purpose in determining the fluid level within tanks. Level sensors operate in different environments that range from vacuums to extremely high pressures and in temperatures that range from below 0oC to very high temperatures. As a result, many types of level sensors have been developed including multi-interface level systems (Bukhari & Yang, 2006). Gas level transmitters may be used to monitor tanks levels and establish whether or not any leakages Conclusion The paper has discussed how monitoring and control can be achieved using various plant equipment in a gas industry. A discussion of the theory for each of the equipments has also been provided together with its contribution to the control and monitoring of the plant. Pumps, control valves and compressors have been found to play important roles in industry as they have significant impact on the movement of gas and other fluids within the plant. They could be used to change speed of transporting the gas, change direction and even regulate pressure and therefore affect the performance of the system. The instrumentation equipments have been found to be majorly used for monitoring of the plant process. By using these equipments, it is possible to assess the general performance of the plant and detection of any problems in the form of leakages and breakages or choking of the pipes and tubes. These may be discovered by monitoring the pressures, flow rates, levels and temperatures of the system and comparing these with the expected values. It must be ensured therefore, in the industry gas plant that the instrumentation equipment are maintained in healthy conditions given the important roles they play within the plant. References Bukhari S.F.A. & Yang W. (2006). Multi-interface Level Sensors and New Development in Monitoring and Control of Oil Separators. Sensors. 6, pp. 380-389 Pirro D.M & Wessol A.A. (2001). Lubrication Fundamentals, Second Edition. Cityyyyyyyyy: CRC Press Hilleret N. (2002). Mechanical pumps. Retrieved on 29th July 2014 from < http://www.chem.elte.hu/foundations/altkem/vakuumtechnika/CERN02.pdf> Boyce M. P. (2012). Gas Turbine Engineering Handbook. Cityyyy: Elsevier Faden J. (2010). Handbook of Modern Sensors: physics, Designs, and Applications. CCCiiityy: Springer Smith P. & Zappe R.W. (2004). Valve Selection Handbook: Engineering Fundamentals for Selecting the Right Valve Design for Every Industrial Flow Application. Cityyy: Elsevier Thomas P. (1999). Simulation of Industrial Processes for Control Engineers. CCCCiiityyyy: Butterworth-Heinemann Gilman G.F. & Gilman J. (2010). Boiler Control Systems Engineering. Ccccityyy: ISA Kalyanaraman D. (2012). Industrial flow meter/flow transmitters. Analog Applications Journal . 2Q, pp. 29 – 32 Krishnamurthy K., Vijayachitra S. & Krishnaswamy K. (2005). Industrial Instrumentation. Cittttytyyy: New Age International Fliegen et al. (2007). Industrial Process Control Valves. Munich: Sv corporate media GmbH Read More