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Boiler Report Jai Khanna 1177724 BE, Biochemical Engineering 24th May 2013 ENMP221-13A

This is my own work and has not copied from or written in collaboration with other person. Signed:

Abstract The investigation for this report is to analyse and observe the efficiency of the boiler system by using the physical data given. The overall system and boundary parts give information on how the energy is being transferred over the entire system. The percentages of combustion energies were evaluated around the different parts of system. The combustion energy for the production of steam was 16.4%, the percentage combustion for the energy lost up the stack was 49.6%, energy lost to drain as hot water was 16.64%, energy lost from the flash steam at the blow down tank was 19.8%, energy used to heat up the air in the lab was 0.57% and the total amount of other heat losses, which was evaluated by the energy balance around the system, it was 35.3%. The energy balance around the overall system gives an energy in of 141.3KW and energy out of 103.5KW, this suggests that the boiler is loosing about 38KW of energy as heat.

Contents

Introduction Assumptions Process flow diagrams and Graphs Overall system Energy Analysis (Bar Graph) Air heater and hot water tank Boiler feed water tank Graph of Change in mass of the boiler feed tank vs. time Boiler furnace Discussion Conclusion References Appendix Calculations Section (Includes: Data Sheet and Psychometric Chart) Part A: Hot water tank/Air heater Part B: Boiler feed water tank with blow down tank Part C: Boiler combustion furnace Part D: Overall System

Introduction Fluids are heated to high temperatures by the use of Boilers, also termed as closed vessels. This Boiler system is a process that involves the intake of gas with a certain amount of energy value and ends up burning it with air. Feed water exchanges heat released from the combustion and gets evaporated as steam. The overall system or the process is divided in to 3 main sections, Boiler combustion furnace, Boiler feed water (including the blow down tank) and the Hot water tank. In present the use of boiler is that it continuously heat a tank of water with the flow of cold water. The purpose and main objective of the investigation was to calculate the mass flows and energy flows of every stream and to evaluate how efficient is the process. By the use of fundamental principles like mass balances and energy balances as it assists briefly in the analysis of each stream. A mass balance is a fundamental method that helps to evaluate the amount going in the stream and the amount coming out. It is a tool that allows to do the conservation of mass. The readings given by the demonstrator helped to do mass and energy balance throughout the system.

Figure 1: inner view of a Boiler

Assumptions Part A: Hot Water Tank and Air Heater Reference temperature is taken to be 273.15K Assuming the mass flow of the stream of E2 is equal to E1, assuming the mass flow of the steam condensate S C is equal to S2 and also assuming the mass flow of the steam hot air outlet A2 is equal to Air inlet A1. The pump present in between the tank and air heater is ignored during the calculation

Part B: Boiler Feed Water Tank The condensate returns are at steady flow rates, i.e. mass flow RC2 = RC1 The data used for calculations is from steam table A-4 Assuming the low quality steam recycle, R S has the same pressure and enthalpy as low quality steam, L1 The steam flow S2 and the flash steam is considered to be saturated vapour.

Part C: Boiler Furnace Assuming the Natural gas (NG) is 100% methane Assuming the Low quality steam, L1 is saturated vapour Reference temperature is taken to be 293.15 K The methane is completely combusted, i.e. mass flow of methane out is 0 There is no CO2 involved in the inlet of firing and not firing.

Part D: Overall System Assuming the overall mass balance around the entire boiler system is at steady state. Assuming the Steam 2, S2 is used as the energy to heat up the tank. Assuming the energy loss between A2 and A1 is used to heat up the air in the lab. The difference between overall energy balance from the inlet and the outlet is used as the energy lost from the entire system.

Discussion Part A: Hot Water Tank and Air Heater While doing the mass and energy balance around the section, the values obtained were relatively close to each other. The mass balance around the tank gave the result to be mass (in) did not equal mass (out) therefore it has an error of margin. The energy balance around tank gave the results to be En (in) did not equal En (out) because in the checklist of the report it mentioned to include a heat loss term. The associated error around the tank was about 9.13KW, which is relatively a big loss of heat. The cause of errors could be because of ignoring and leaks or energy losses on the surfaces of the pipes.

The mass balance around the air heater was entirely equal (in) = (out) and no errors were associated. The energy balance around the air heater exists a minor heat loss of about 0.09KW, which is relatively small compare to the tank. The reason of the heat loss occurred in the tank and air heater could also be due to open tank and hot surfaces.

Part B: Boiler Feed Water In this section, the mass balance around the boiler feed water tank was (in) = (out) there were no errors associated to be in the mass flow of the system. The main aspect of the system’s error could be because of assuming the boiler feed tank as a rectangular shape instead of taking as cylindrical. Practically it would not affect in the analysis of the boiler feed water tank but there will be errors correlated in theoretical analysis. The energy balance En (in) did not equal En (out) because the checklist for the report includes a heat loss of 1KW therefore it correlates with an error of 0.98 KW. The errors can also be associated with system because of inaccuracy, equipment calibration and human errors.

Around the chamber where three streams are interacted together was evaluated because to find the mass flow of the unknown Condensate return 1, R C1. The mass balance around the chamber gives the value to the R C1 of 0.000108 kg/s. The energy balance results with an error of 0.2 KW because of pressure change in steam S1 and steam S2. The assumptions were made that the pressure of S 1 is equal to R C1. The steam quality (X) of the low quality steam is about 10.6% of vapour compared to 89.4% of liquid in the line.

Rounding errors Assuming cylindrical Shape as rectangle

Part C: Boiler Furnace In the Boiler Furnace part, the mass and energy balance was conducted when the furnace was firing, not firing and the average of both. Assuming the natural gas to be 100% methane, this was done to make the calculations easy for the furnace. The heat transfer was between the boiler furnace and the steam production. The mass flow for the firing gives a loss of 0.00031Kg/s where as the mass flow for not firing resulted to be equal, it has no loss because the natural gas is not being pass through the pipes and not getting burned, only the flue gases were being travelled. The energy balance for firing gives a loss of 47.69KW because large amount of (NG) is burned. The energy balance for not firing gives a loss of 45.17KW, these errors within the system causes the overall efficiency to get low. Another contribution that allows errors to fall in can be from the systematic errors, readings from the equipments could have some amount of uncertainty, but this would not be accounted as one of the main aspects.

Part D: Overall System In this section, there was an overall mass balance and energy balance conducted to find the errors between the streams going in and out. The overall mass balance gives a loss of 0.055Kg/s that does not acts as a major difference. The overall energy balance gives a loss of 38.14KW, which is the energy lost as heat from the boiler system. Also there sensitive stream flow rates which was evaluated by an increase of 10%. Methane was comparatively the most sensitive stream because it affects the heat of combustion and increased it by 9.69% where as other streams like the cold feed water, which was increased by 10% therefore affected the boiler feed water because they both are linked. The boiler feed water was increased by 8.85%. In theory increasing the amount of methane in furnace will then tend to produce more steam and it would also increase the overall efficiency of the boiler.

Conclusion To conclude this investigation the boiler system has major and minor heat losses because of the inconsistency, which can be occurred by the presence or errors in all the different streams of the system. The whole research around the system was done to do an evaluation over the entire boiler system by its given boundaries, it defines each part for the boiler system precisely. Using the fundamental principles of mass and energy balance it gives assistance to the students to calculate the mass and energy flows for each stream. There have been calculations done on each part of the system to check for the reliable results. As per the conclusion, the percentage of the combustion energy used to heat the tank was about (16.40%), lost to drain as hot water in the boiler room was about (16.64%), lost up the stack in the flue gases was about (49.60%), lost as flash steam from the blow down tank was about (19.8%), energy used to heat up the air in the lab was about (0.57%) and the overall amount of other heat losses was about (35.30%) which includes the hot surfaces and evaporation. This relates to the overall efficiency of the boiler system is that it looses energy in large amount including all the parts.

The heat losses around the system has been occurred as a major reason of the system to have a lower efficiency because the flow rates in each stream does not equal, this involved discrepancy in the overall results for the boiler system. In real world the efficiency of 100% cannot be possible for a system because there are lots of irreversibility such as friction involved in all types of machines. To construct a device operating in a thermodynamic cycle, which produce no effect other than work output can have the maximum efficiency but in real world it is not achievable.

References Cengel, Y. A., and Boles, M.A. (2002). Thermodynamics An Engineering approach (4th ed.).

ENMP221-13A (HAM) Engineering Thermodynamics Laboratory Manual (2013). Faculty of Science and Engineering...