Design and Development of an ARM Platform Based ...

2013 IEEE Symposium on Industrial Electronics & Applications (ISIEA2013), September 22-25, 2013, Kuching, Malaysia

Design and Development of an ARM platform based Embedded System for Measurement of Boiler Efficiency *Chayalakshmi .C.L, **D.S. Jangamshetti

Savita Sonoli

*Dept. of Instrumentation Technology, ** Dept. of Electrical and Electronics Engineering, Basaveshwar Engineering College, Bagalkot, Karnataka, India. *[email protected], **[email protected]

Dept. of Electronics and Communication, RYM College of Engineering , Bellary, Karnataka, India. [email protected]

repair of a boiler. The steam system collects and controls the steam produced in the boiler. Steam is directed through a piping system to the point of use. Throughout the system, steam pressure is regulated using valves and checked with steam pressure gauges. The fuel system includes all equipment used to provide fuel to generate the necessary heat. The equipment required in the fuel system depends on the type of fuel used in the system. Conventional system of finding boiler efficiency is more prone to errors; because of the involvement of an operator in collecting data and processing it using complicated mathematical equations. The following are the steps to calculate the efficiency by the human operator: • The operator has to note parameters like temperature of feed water, steam pressure. • Then the operator has to use steam table to get the enthalpy of feed water, specific enthalpy of water and specific enthalpy of evaporation, which are required to calculate the enthalpy of steam. • Then all the values are to be substituted in the equation for finding boiler efficiency.

Abstract— Boiler is an integral component of any process industry. The boiler efficiency probably degrades due to bad operation and lack of maintenance. So, performance analysis of the boiler has to be carried out regularly. Performance of a boiler is measured in terms of efficiency. Efficiency is one of the important parameters of a boiler, which gives information about its operating condition, heat generation from it and heat loss. Real time monitoring of efficiency helps an operator to know the boiler efficiency continuously. Real time measurement of efficiency would help in evaluating the performance of the boiler, which is necessary for taking energy conservation action in industry. This paper presents design and development of an embedded system, based on Advanced Reduced Instruction Set Computing Machine (ARM) platform to monitor the efficiency using input-output method. The developed system is tested using the technical data of a thermal power station.

Key Words— Performance analysis, Boiler Efficiency, InputOutput method, ARM.

I. INTRODUCTION Boiler plays a very important role in any process industry. It is a device which converts water to steam, as water is cheaper than any other liquid that can be used for transferring the heat to a process. For conversion it uses heat which is generated due to combustion. Boilers can generate steam with various pressure and temperatures, depending upon the fuel used and the type of equipment. Usually the fuel used for combustion is coal, natural gas, oil etc. The volume of steam is higher and the force produced is almost same as the force exerted by gun powder. So, boilers are to be treated with care as it is a dangerous device [1]. Pressurized steam can be used to produce work in many applications such as expanding and retracting a piston, to expand gasses in a cylinder or environmental heating. In many process industries steam or super heated steam is considered as an energy source. Usually the energy efficiency is the major performance analyzing parameter for the boilers. The schematic diagram of an industrial boiler is as shown in Fig. 1. The heat generated can be transferred to the process in any of the three methods like conduction, convection or radiation [2]. The boiler system comprises of feed water system, steam system and fuel system. The feed water system provides water to the boiler and regulates it automatically to meet the steam demand. Various valves provide access for maintenance and

978-1-4799-1124-0/13/$31.00 ©2013 IEEE

The manual effort to calculate the boiler efficiency is nullified by the system. With this system, an operator is able to know the boiler efficiency more accurately, as the system collects the data from the sensors. Processing is done in ARM7 processor which works at a very high frequency in several megahertz. ARM7 processor is considered as a system on chip and is suitable for industrial process control applications. ARM7 is the best choice due to its high performance, low power consumption, low cost and small size [3]. II. BOILER EFFICIENCY A. Need for Monitoring Boiler Efficiency Boiler is the major component in generating electricity in India [4] [5]. Efficient boiler operation has always been critical in power plant. Determination of efficiency on regular basis helps to find variation of boiler efficiency from its best value. Hence, the performance of the boiler has to be carried out regularly to know more about the healthy condition of a boiler, which is pre requisite for energy conservation action in industry. Lower performance results in an increase in the cost of production [6]. Performance is decided based on the

39

2013 IEEE Symposium on Industrial Electronics & Applications (ISIEA2013), September 22-25, 2013, Kuching, Malaysia

efficiency. Performance of a boiler degrades over the time because of aging, resulting in higher heat rate, CO2 emissions and operating costs with lower reliability and in some cases reduced output. After few years of neglect, it may reach the point where significant investment is required to rehabilitate the boiler plant and bring it as close as possible to the design performance. In general, majority of the plants were designed at a time when the plant’s production was the critical operating parameter. Now a day, the operation of the boilers is based on the use of certain variables, derived from the suppliers or from the accumulated experience of the operators, which may lead to human error and time consuming.

various boiler losses like boiler loss due to dry flue gas, loss due to hydrogen in fuel, loss due to moisture in fuel, loss due to moisture in air, loss due to carbon monoxide, loss due to surface radiation, un-burnt losses in fly ash, un-burnt losses in bottom ash are to be calculated using various equations. Then the following equation is for finding the efficiency: Percentage Boiler Efficiency = 100 – (sum of all boiler losses). Hence, direct method is easier than indirect method. In direct method, boiler efficiency is determined using Eq. 1 [7]. {Q × (H − h)} (1) % Boiler Effeciency = η = × 100 q × GCV Where, Q H h q GCV

= Quantity of steam generated per hour (kg/hr) = Enthalpy of steam (kJ/kg) = Enthalpy of feed water (kJ/kg) = Quantity of fuel used per hour (kg/hr) = Gross Calorific Value of the fuel (kJ/kg).

The enthalpy of feed water and steam are calculated using Eq. 2 and Eq. 3 respectively. Enthalpy of feed water = h (kJ/kg) = CW (tf – t0)

(2)

Where, CW = Specific heat of water = 4.19 kJ/kg °C tf = Mean feed water temperature (°C) t0 = Reference temperature = 0°C. Enthalpy of steam = H (kJ/kg) = hf + χ hfg

(3)

Where, hf = Specific enthalpy of water (kJ/kg) χ = Dryness fraction hfg = Specific enthalpy of evaporation (kJ/kg).

Fig. 1: Schematic of an industrial boiler [6]

Hence, there is a necessity to introduce embedded based system to monitor the boiler efficiency on a real time basis. This reduces the involvement of operator’s intelligence, experience and increases the effectiveness of estimation.

The following is the technical data of an Ukai Thermal Power Station [1]. This data is used for verification of our system. Design Data of 200 MW Boiler is given below: • Boiler type: Direct tangentially coal fired, balanced draught, natural circulation • Designed fuel : Coal • Mass of coal burnt (q) : 85 T/hr • Mass of steam generated (Q) : 600 T/hr • Coal Fixed carbon : 39 % Volatile matter : 25 % Moisture :8% Ash : 28 % • Gross Calorific Value : 4900 kcal/kg GCV in terms of kJ/kg : 20501.6 kJ/kg • Mean feed water temperature : 35 °C • Pressure of steam : 131.9 kg/cm2 Pressure of steam in terms of bar : 129.5 bar

B. Calculation of Boiler Efficiency The boiler efficiency is calculated using the two methods: 1) Direct method or input output method and 2) Indirect method or Heat loss method. Direct method is easier than indirect method. In direct method, efficiency is calculated as the ratio of heat output to heat input. Heat output is defined as the heat absorbed by the working fluid and heat input is defined as the chemical heat in fuel and plus the heat credit [4]. In direct method the energy gain of the working fluid is compared with the energy content of the boiler fuel. But, in indirect method the efficiency is the difference between the losses and the energy input. For direct method, the parameters needed to find efficiency is less and also the mathematical equation is simpler. But, if indirect method is used for the calculation of boiler efficiency, then many parameters are to be measured. In indirect method,

40

2013 IEEE Symposium on Industrial Electronics & Applications (ISIEA2013), September 22-25, 2013, Kuching, Malaysia

changes depending on the temperature to which it is exposed. The change in resistance for every 1 °C is 0.384 Ω. Figure 3 shows the signal conditioning circuits used to acquire the signal of an RTD. This includes Wheatstone bridge followed by voltage follower and Instrumentation amplifier. The output of RTD is connected to a Wheatstone bridge, which converts change in resistance to change in voltage. The bridge is balanced at 0 °C. Hence, at 0 °C the output voltage of Instrumentation amplifier is 0 V. When the feed water temperature is 35 °C, the resistance of RTD is 113.37 Ω. The differential bridge output voltage is 0.155 V, as the voltage at one end of the Wheatstone bridge is 2.5 V and at the other end, voltage is 2.345 V. The gain of an Instrumentation amplifier is 10. Therefore, the output voltage of an Instrumentation amplifier is 1.55 V. The circuits are developed in Microcap 10 simulation software. The output voltage values are approximated to two decimal digits. The signal conditioning hardware circuit is constructed using precision operational amplifier OPA703. The offset voltage of OPA703 is 160 µV. The output values of hardware circuit are verified with the simulated output. Figures 4 and 5 show the feed water temperature measured with thermometer and the complete experimental set up respectively. Table I shows the theoretical and practical values of output of Instrumentation amplifier for different feed water temperature. Output voltage signal from Instrumentation amplifier is given to the channel 0 of inbuilt 10 bit ADC of LPC2129.

For a steam pressure of 130 bar, the specific enthalpy of water and evaporation is obtained from the steam table [9] and are as below: hf = 1513.5 kJ/kg; hfg = 1130.7 kJ/kg Therefore, H = hf + χ hfg H = 1531.5 + (0.85)(1130.7) = 2492.595 kJ/kg Enthalpy of feed water = h = 4.18(35 – 0) = 146.3 kJ/kg Hence, after substituting all the values in Eq. 1, the efficiency of boiler is obtained as % η = [{600 (2492.595 – 146.3)} / {85(20501.6)}] × 100 Boiler efficiency = % η= 80.77 % III. IMPLEMENTATION The direct method of evaluating the boiler efficiency is implemented by measuring the feed water temperature and the pressure of the steam coming out from the boiler. Resistive Thermal Device (RTD) is used to measure the temperature and a pressure transmitter is used for the measurement of the steam pressure. Boiler efficiency is evaluated using LPC2129 which is one of the products from NXP semiconductor and is based on ARM7TDMI-S platform. A. ARM7TDMI-S An embedded ARM platform is designed and implemented to calculate the efficiency of a boiler using direct method. An ARM7TDMI-S, a member of ARM family of general purpose 32-bit microprocessor is suitable for this application. The ARM family offers high performance with very low power consumption [10]. The ARM architecture is based on the RISC principles. The RISC instruction set and decoder mechanism is simpler than those of CISC, giving a high instruction throughput and an excellent real time interrupt response. ARM uses pipelining method to increase the speed of flow of instructions to the processor. ARM7TDMI-S supports ARM instructions of 32 bit and Thumb instructions of 16 bit. Thumb instruction set enhances the code density. Some of the features of LPC2129 are as follows [11]: • 16/32-bit ARM7TDMI-S microcontroller in a 64 or 144 pin package. • Four/eight channel (64/144 pin package) 10-bit A/D converter with conversion time as low as 2.44 ms. • Two 32-bit timers (with 4 capture and 4 compare channels), PWM unit (6 outputs), Real Time Clock and Watchdog.

RTD PT100 as a boiler feed water temperature sensor and signal conditioning circuit

L P C 2

LC D (16 ×2)

1 Boiler Steam Pressure transmitter as a pressure sensor and current to voltage converter

2 9

Fig. 2: Block diagram of the system

A pressure transmitter is used as a pressure sensor to measure the pressure of steam coming out from the boiler. The range of output signal from the pressure transmitter is between 4 to 20 mA. This signal is converted to voltage with current to voltage converter. The feedback resistance used for conversion is 150 Ω, so that when current input is 4 mA, the voltage output from current to voltage converter is 0.6 V and at 20 mA the voltage is 3 V. The voltage signal is then given to the channel 1 of internal ADC. ARM processor is operated at 12 MHz. For every 1 sec, the data from an internal ADC is read, so that the output data can be updated at every 1 sec. This time interval is suitable because the temperature of feed water and pressure of steam will not change instantaneously.

B. Block Diagram Figure 2 shows the block diagram of the system. Resistance Thermometer Device (RTD) is suitable for the measurement of boiler feed water temperature. The resistance of RTD changes with change in temperature. It is necessary to measure the temperature of feed water to find its enthalpy. RTD PT100 is a sensor whose resistance is 100 Ω at 0 °C and 138.4 Ω at 100 °C. PT100 uses platinum as a metal, whose resistance

41

2013 IEEE Symposium on Industrial Electronics & Applications (ISIEA2013), September 22-25, 2013, Kuching, Malaysia

LPC2129 is used for calculation of enthalpy of feed water, enthalpy of the steam and the efficiency of the boiler. Program is developed using Keil software. Along with main program, subroutines are implemented to generate appropriate time delay, to initialize LCD and to send command and data to the LCD. The simulated software is showing an output voltage of 1.55 V for the feed water temperature of 35 °C. Figure 5 shows the experimental results of Instrumentation amplifier at 35 °C. Figure 6 shows the flow chart for implementation of the system. Ports are initialized for connecting LCD and for providing the analog input to the inbuilt ADC of LPC2129. Then the digital code corresponding to the feed water temperature is read through channel 0 and the digital code corresponding to steam pressure is read through channel 1 of ADC module. According to the steam pressure, the specific enthalpy of water and specific enthalpy of evaporation is obtained from the look up table. Then the enthalpy of feed water and steam is calculated from appropriate equations. Finally the boiler efficiency is calculated. Table II gives the boiler efficiency values for different feed water temperatures. It is observed from the table that, as the temperature of feed water varies from 25 °C to 45 °C the efficiency varies from 79.33 % to 82.21 %. To get more efficiency, the feed water temperature must be high. Figure 7 shows the display of boiler efficiency value at a feed water temperature of 35 °C and the steam pressure of 130 bars in the LCD of developed system. The practical values obtained with the developed embedded system match with the theoretical values presented in section II. If the specific enthalpy values are stored in the look up table, for a particular range of steam pressure, then this system can be used to measure the boiler efficiency in any industry. TABLE I. INSTRUMENTATION AMPLIFIER OUTPUT FOR DIFFERENT FEED WATER TEMPERATURE Feed water temp in °C 25 30 35 40 45

RTD resistance in Ω 109.6 111.5 113.4 115.3 117.2

Wheatstone Bridge O/P in mV

Instrumentation Amplifier O/P in V

Theoretical

Practical

Theoretical

Practical

114.5 135.9 156.9 177.6 197.9

114.1 136.2 155 176 197

1.14 1.36 1.56 1.77 1.97

1.14 1.35 1.55 1.76 1.98

Fig. 3: Signal conditioning circuit for the measurement of feed water temperature

TABLE II. BOILER EFFICIENCY FOR VARIOUS FEED WATER TEMPERATURES Feed water temp in °C 25 30 35 40 45

% Boiler Efficiency 79.33 80.05 80.77 81.49 82.21 Fig. 4: Thermometer reading

42

2013 IEEE Symposium on Industrial Electronics & Applications (ISIEA2013), September 22-25, 2013, Kuching, Malaysia

IV. CONCLUSION In this paper, the design and development of an embedded system for performance evaluation of a boiler by finding the boiler efficiency is presented. Boiler efficiency is obtained using direct method. The direct method of obtaining efficiency of a boiler is simpler as number of parameters measured is less. The only requirement is to measure the heat supplied to the boiler and heat absorbed by the water. The software is developed using Keil version 4. The outputs obtained with the system are verified with the earlier technical data [1]. This real time measurement and monitoring of the boiler efficiency helps to know continuously the operating conditions of a boiler. The performance characteristics of a boiler can be used to optimize its operation and also to enhance its efficiency with reduction in fuel consumption.

Fig. 5: Experimental setup START

Initialize ports for ADC and LCD

REFERENCES [1] Sunit Shah, D.M. Adhyaru, “Boiler Efficiency Analysis Using Direct Method,” IEEE International conference on Current trends in technology, NUiCONE 2011, 978-1- 4577-2168-7/11. [2] Brad Buecker, “Basics of Boiler and HRSG Design,” Pennwell Books, 2002. [3] Daogang Peng, Hao Zhang, Kai Zhang, Hui Li, Fei Xia, “Research and Development of the Remote I/O Data Acquisition System Based on Embedded ARM Platform,” IEEE International conference on Electronic Computer Technology, 2009, 978-0-7695-3559-3/09. [4] “Electrical system,” Bureau of Energy Efficiency, http://www.enercon.gov.pk/images/pdf/3ch1.pdf [5] “Power India,” Department of Industrial Policy and Promotion, Ministry of Commerce and Industry, Government of India, http://dipp.nic.in/English/Investor /Investers_Guidlines/Power.pdf [6] “Computerized Information Technology,” http://www. cituk online.com/acatalog/Thermal_Power_Plants .html [7] “Energy Performance Assessment of Boilers,” Bureau of Energy Efficiency. [8] “Boilers,” Bureau of energy Efficiency. [9] P.K. Nag, “Engineering Thermodynamics,” 3rd Edition, Tata Mc Graw Hill. [10] Chayalakshmi C.L, D.S. Jangamshetti, Savita Sonoli, “Real Time Remote Monitoring and Measurement of Loss due to Dry Flue Gas for an Industrial Boiler,” 3rd International Conference on Advances in Power Electronics and Instrumentation Engineering, vol.150, pp.490-495, ISSN:1876-1100, ISBN:978-1-4614-3362-0, August 2012, Springer-Verlag Berlin Heidelberg. [11] “LPC2119/2129/2194/2292/2294 User Manual,” Philips Semiconductor, 2004.

Read the temperature of feed water through channel 0 and the pressure of steam coming out through channel 1 of an internal 10 bit ADC Get the specific enthalpy of water and specific enthalpy of evaporation from look up table Calculate enthalpy of feed water and enthalpy of steam using Equations 2 and 3 Calculate percentage Boiler efficiency Display Efficiency

STOP

Fig. 6: Flow chart of the system

Fig. 7: Boiler efficiency when feed water temperature is 35°C.

43