AUTOMATION OF BOILERS USING LABVIEW

Transcription

1 I J L S C M 4(1), 2012, pp AUTOMATION OF BOILERS USING LABVIEW A. MICHAEL SIDDHARTHA AND S. NAVEEN KUMAR Under Graduate Student, Department of Electronics and Communication Engineering Thiagarajar College of Engineering, Madurai , Tamil Nadu, India michaelasiddhartha@gmail.com; naveenkumar1157@gmail.com Abstract: This paper outlines the various stages of operation involved in the conversion of a manually operated boiler towards a semi automated boiler. Over the years the demand for high quality, greater efficiency and automated machines has increased in this globalised world. The initial phase of the paper focuses on passing the inputs to the boiler using DAQ. The parameters are compared with standard norms and an indication is given through the system if the parameters do not fall within the safe region. The paper mainly focuses on the automation of two critical parameters feed water level and steam drum temperature.. Whenever the feed water level goes below a critical level, the valve opens to feed water and similarly when the temperature in the water walls increase, the water from the steam drum is sent to the water walls to produce steam. Thus the temperature in the boiler is constantly monitored and brought within a safe limit. Keywords: flow sensor LabVIEW, level sensor pressure sensor, temperature sensor. 1. INTRODUCTION Automation is the use of control systems and information technologies to reduce the need for human work in the production of goods and services. In the scope of industrialization, automation is a step beyond mechanization. Whereas mechanization provides human operators with machinery to assist them with the muscular requirements of work, automation greatly decreases the need for human sensory and mental requirements as well. Automation plays an increasingly important role in the world economy and in daily experience. Boilers are required to maintain maximum steam generation efficiency, maximum reliability, and comply with both stringent air emission and safety regulations. To achieve this goal we need modern control hardware and softwar e. In today s competitive ma rket minimization or reduction of operating costs is a valid method to increase profitability. Reducing fuel expenses associated with the boilers can directly impact manufacturing costs. By automating the control of Boiler using LabVIEW, the human errors in calculations and the need of skilled operators can be minimized. The values such as temperature, pressure measured are hived away. This method is cost effective and reduces the time consumed for operating the Boilers [1]. 2. REVIEW OF LITERATURE PLC applications are extensively used in industry to control and facilitate repetitive processes such as manufacturing cell management, fly-by-wire control boiler automation. But automating boilers using PLCs have the following disadvantages. Programmable controllers are not equipped with enough memory to store big amounts of data, in this case a communication system need to be more developed. There is too much work involved in connecting wires. Ther e is difficulty with changes or replacements. It s always difficult to find errors; and require skillful work force. When a problem occurs, hold-up time is indefinite, usually long. If the plc goes down the whole boiler is down. 3. OVERVIEW OF A BOILER 3.1. Sensible Heat Addition Feed Water Pump The first step is to get a constant supply of water at high pressure into the boiler. Since the boiler is always

2 50 A. Michael Siddhartha and S. Naveen Kumar at a high pressure. Boiler feed water pump pumps the water at high pressure into the boiler from the feed water tank Pre-Heating Feed water heaters use the steam extracted from the turbine, and adds a part of the sensible heat even before the water enters the boiler. This improves the efficiency of the boiler Economizer Most of the sensible heat is absorbed in the Economizer. The economizer consists of a set of coils made from steel tubes and is located in the tail end of a boiler. The hot gases leaving the boiler furnace, heat the water in the coils. The water temperature is slightly less than the saturation temperature. From the economizer the water is fed to the drum [2]. Economizers offer the following advantages: Fuel economy Longer life of the boiler Increase in steaming capacity 3.2. Latent Heat Addition Drum The drum is a large cylindrical vessel that functions as the storage and feeding point for water and the collection point for water and steam mixture. This is the largest and most important pressure part in the boiler and weighs in the range 250 Tons for 600 MW power plant Water Walls Boiling takes place in the Water Walls which are water filled tubes that form the walls of the furnace. Water Walls get the water from the downcomers which are large pipes connected to the drum. As the water heats up in the furnace a part of the water in the water-wall tubes becomes steam. This water steam mixture has a lower density than the water in the downcomers. This density difference creates a circulation of water from the drum, through the downcomers, water walls and back to the drum. Steam collects at the upper half of the drum. The steam is then sent to the next sections. The temperature in the drum, downcomers and water wall is at the saturation temperature Super Heater Steam from the drum passes to the Super Heater coils placed in the Flue gas path. The steam temperature increases from the saturation temperature till it reaches the maximum temperature required for operation. The superheated steam then finally goes to the turbine. Final Super heated steam temperatures are in the Range of 540 to 570 C for large power plants and Superheated steam pressures are around 175 bar. The Super Heater affects improvement and economy of the boiler in the following ways. The super heater increases the capacity of the plant. Eliminates corrosion of the steam turbine. Reduces steam consumption of the steam turbine Reheater Steam from the exhaust of the first stage turbine goes back to the boiler for reheating and is returned to the second stage. Reheater coils in the flue gas path does the reheating of the returned steam. The reheat steam is at a much lower pressure than the super heated steam but the final reheater temperature is the same as the superheated steam temperature. Reheating to high temperatures improves the output and efficiency of the Power Plant. Final Reheater temperatures are normally in the range of 560 to 600 C. Reheat steam pressures are normally around 45 bar Coal System Coal received from the mines is stored in the coal yard adjacent to the power plant. It is then conveyed on a daily basis to the boiler and stored in a Coal Silo. Coal feeders continuously feed the required amount of coal to the Coal Pulverisers Coal Pulverisers Coal Pulverisers grind the coal to a very fine powder so that it burns easily. Pulverisers have steel rollers or steel balls which crush the coal between them into a fine powder. This powder is easy to burn. Coal contains moisture. Hot air form the Primary air fans dry the coal in the pulverisers. This makes the combustion efficient. This air also carries the dry coal powder from the pulverisers to the burners in the boiler furnace. In the burners the coal powder is mixed with the required amount of Combustion air and set ablaze [3].

3 Automation of Boilers using Labview Air System Correct amount of air is the most essential ingredient for Combustion. More air or less air both makes the combustion process inefficient Forced Draft Fan Forced Draft Fan supplies most of the Combustion air. This fan takes air from the atmosphere and blows it into the furnace through air ducts. The Air Heater heats the air before it enters the Furnace Air Heater Air Heater utilizes the heat of the hot flue gases that leave the boiler to heat the combustion air. The air heater improves the efficiency of combustion. The Air Heater works on the regenerative principle. Steel plates alternatively placed in the hot flue gas path and then in the air path heats the cold air entering the Air Heater Primary Air Fan Primary Air Fan supplies the air to the pulverisers for drying and transporting coal. This air called the Primary air. The Primary Air is also heated in the Air Heater Flue Gas System Coal burns in the furnace giving out heat and forming flue gases Induced Draft Fan The hot flue gases from the furnace is drawn out by the Induced draft fan. The gases passes through the various heating surfaces of the boiler, the Electrostatic Precipitator and discharges to the atmosphere at the top of the stack. The Induced Draft Fan is normally located adjacent to the Stack [4] Electrostatic Precipitators Electrostatic precipitators capture the fly ash in the flue gases without letting them out into the atmosphere. High voltage electrodes placed in the gas path ionize the ash particles which collects on collecting electrodes and falls into ash hoppers [5] Stack Stack or the Chimney disperses the hot gases and any other particles at a great height. The height enables a very large dispersion area and regulates emission concentrations at ground levels to the level acceptable to humans and vegetation. Stack heights for large power plants are around 250 to 280 meters Balanced Draft The Forced Draft fan and the Induced Draft fan operate in such a way that the air pressure in the furnace is at zero pressure i.e. at atmospheric pressure. This is called the Balanced Draft system Ash System Ash is the inert matter in coal and is the residue after combustion. This has to be collected and disposed off without letting it out into the atmosphere. A part of the ash, around 15 % collects as Bottom ash at the bottom of the furnace. The other part collects as Fly ash in the Electrostatic Precipitators. The collected ash is then transported to disposal yards or storage silos. 4. CRITICAL CONTROL PARAMETERS IN BOILER 4.1. Level Control Steam Drum level De-aerator level Hot well level Feed water level 4.2. Pressure Control Force draft pressure Induced draft pressure Steam drum pressure Deaerator pressure Turbine inlet steam pressure Balanced draft pressure Pressure of Primary Air fan 4.3. Flow Control Air flow Steam flow Water flow 4.4. Temperature Control Deaerator temperature Steam drum temperature Underbed boiler temperature

4 52 A. Michael Siddhartha and S. Naveen Kumar Turbine inlet steam temperature Flue gas temperature [6]. drum is also filled with water. Thus it keeps the boiler from bursting. 5. USING LABVIEW Here we have developed an application in such a way that the critical parameters as mentioned are monitored at regular intervals of time. When the application is run the thermocouples, flow sensors, level sensors and pressure are initialized using DAQ and all the above stated parameters are measured and recorded. We suggest NI 9213, NI 9205, NI 6624 DAQ cards [7]. The level of steam drum, de-aerator, hot well, Force draft pressure,induced draft pressure, Steam drum pressure, Deaerator pressure, Turbine inlet steam pressure, balanced draft pressure, Air flow, Steam flow, Water flow, Deaerator temperature Steam drum temperature, Underbed boiler temperature, Turbine inlet steam temperature, Flue gas temperature are compared with the standard norms and if it is not equal to the standard values an indication will be shown. We use LEDs for indication and a text message is also displayed. By seeing this indication the operator can raise the temperature and pressure by increasing the coal flow. The total execution time to process a single set of data is on an average of 40ms. The average time consumption of processing data is measured by averaging the time taken for processing 10 sets of data. The NI components used also cause a delay of 55ms seconds for sending the input data. Thus the total time delay for processing a set of data is around 95ms. The loop accepts input every second and calculates the output Automation of Feed Water Level The feed water level is constantly measured. When ever the water level goes below 20% of the total tank capacity the water inlet valve gets opened to fill in the water Automation of Steam Drum Temperature When ever most of the water in the water wall gets converted into steam, the temperature in the water wall and the steam drum also increases. When it increases beyond a safe limit the water from the steam drum flows to the water walls at a specified rate which can be specified by the boiler administrator and the steam Figure 1: Front Panel 6. ADVANTAGES 6.1. Benefits of using Virtual Instrumentation Virtual Instrumentation is the use of customizable software and modular measurement hardware to create user-defined measurement systems, called virtual instruments. Traditional hardware instrumentation systems are made up of predefined hardware components that are completely specific to their stimulus, analysis, or measurement function. Because of their hard-coded function, these systems are more limited in their versatility than virtual instrumentation systems. The advantage of using virtual instrumentation over hardware instrumentation is that software is used to replace a large amount of hardware. The software enables complex and expensive hardware to be replaced by already purchased computer hardware. Automating the boilers helps in avoiding human errors in calculations. It improves the safety of the workers by avoiding them working around dangerous equipments.

5 Automation of Boilers using Labview 53 Measurements made are more precise. The data are continuously logged. 7. FUTURE ACTION PLAN At present we have automated the feed water level monitor and the steam drum temperature. In future we would extend the automation to all the critical parameters leading to a completely automated boiler. In future the system would be upgraded to find faulty sensors also using redundant logic. For example to determine the temperature of steam drum three temperature sensors would be used and the output of the three sensors would be compared. If the three sensors give the same output the output value would be used for processing. If a particular sensor fails then voting logic would be applied to generate the output. The output value produced by majority of the sensors would be used for processing [8]. 7. CONCLUSION The most important aspect of any power plant is the boiler control. Several techniques can be implemented to control the boiler in power plant. The method that has to be used relies on varied objectives like superior quality, increased efficiency, high profit and other such points depending upon the purpose of the company that implies it. With the prime objective of catering to these necessities and the needs of the industrial sector, significance has been given to automation. Our paper will bring about a cost and time effective alternative for the industries by accurate measurements and control of boilers using LabVIEW. The main purpose of the project is to automate the boiler control using LabVIEW thereby requirement of operators can be reduced. Finally saying this project is a small step towards the conversion of entire system to a fully automated one. References [1] Boiler Plant Automation available at [2] Coal Power Plant available at power-plant/water-and-steam-system-a-power-plantboiler-work/ [3] Pulverising Mill available at explore_drax/power_station/?id=1867 [4] Boiler Air and Flue Gas system available at rs.c om/f orum/mech anic alautomobile-engineering/39174-boiler-air-flue-gassystem.html [5] Electrostatic Precipitators available at en.wikipedia.org/wiki/electrostatic_precipitator [6] K.Gowri Shankar, Control of Boiler operation using PLC SCADA, Proceedings of the International Multi Conference of Engineers and Computer Scientists 2008 Vol II IMECS 2008, March, 2008, Hong Kong. [7] NI Components available at [8] Voting logic available at Redundancy_(engineering)