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Performance Analysis of Separating and Throttling Calorimeter to Determine

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Performance Analysis of Separating and Throttling Calorimeter to Determine
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  41 PERFORMANCE ANALYSIS OF SEPARATING ANDTHROTTLING CALORIMETER TO DETERMINEQUALITY OF STEAM ON THERMAX DIESELFIRED WATER TUBE BOILER  Abstract In present study the Separating & Throttling Calorimeter set up is developed on Thermax diesel fired water tube Boiler (Three pass Reverse Flue coil type steam generator) in Thermal Power Laboratory and experimentation is carried out to determine the quality of steam (The  percentage by weight of steam in a mixture of steam and water) passing through the steam main. The limitation of our experimentation is the wet steam. The calorimeter results are not applicable to dry and superheated steam. The analytical analysis is also carried out using steam table. The effect of parameters like steam temperature, steam pressure, water outlet temperature of economizer, Fuel pressure, exhaust gas temperature, water and fuel flow rate on quality of steam is a recorded. Keywords : Steam, Dryness Fraction, Boiler Efficiency, Separating and Throttling Calorimeter  1. Introduction Steam is the major source for power generation in steam engines or steam turbine. Steam is produced from water by combustion of fuel in a boiler and employed for heating the building in cold weather, in the textile industries for sizing and bleaching, sugar industries, chemical industries etc. The primary requirements of steam generators or boilers are (i) Water must be contained safely. (ii)The steam must be safely delivered in desired condition as regards its pressure, temperature, quality and required rate. The presence of moisture in steam causes a loss of heat from the feed water temperature to the steam temperature. The boiler consists of a membrane coil fitted in a shell which in turn is enclosed by an air jacket. The coil forms the combustion chamber (furnace). Burning fuel generates heat which produces steam. High pressure pumps supply water and fuel to the boiler and air is supplied by a blower fan. Steam is generated within a few minutes after firing the unit[1]. *R.G.Bodkhe, Y. Y. Nandurkar, S. S. Akant, S. L. Bankar *r_bodkhe@rediffmail.com Department of Mechanical Engineering,Yeshwantrao Chavan College of Engineering, Nagpur (India) 2. Construction of test set up The boiler is bolted on a bottom chassis. Blower, control panel and other panels are also bolted on the chassis. The structure is supported from above by a top chassis. On both sides are hinged doors. Ladder is in the front, adjacent to the control panel. The utility valves are on the rear side. At the center of the boiler is the coil made of boiler quality carbon steel tubes. The coil is enclosed by a pair of concentric shells. This pair of shells forms an air jacket around the coil[1]. 2.1 Separating calorimeter  The separating calorimeter is a vessel used initially to separate some of the moisture from the steam, to ensure superheat conditions after throttling. The steam is made to change direction suddenly; the moisture droplets, being heavier than the vapor, drop out of suspension and are collected at the bottom of the vessel.It consists of two concentric chambers, the inner chamber and the outer chamber, which communicates with each other through an opening at the top. As the steam discharges through the metal  basket, which has a large number of holes, the water particles due to their heavier momentum get separated from the steam and collect in the chamber. The comparatively dry steam in the inner chamber moves up and then down going through the annular space between the two chambers and enters the Throttling Calorimeter [3]. 2.2 Throttling calorimeter  The throttling calorimeter is a vessel with a needle valve fitted on the inlet side. The steam is throttled through the needle valve and exhausted to the condenser. Suppose M kg of wet steam with a dryness fraction of x (state A) enters the separating calorimeter. The vapor part will have a mass of xM kg and the liquid part will have a mass of (1-x)M kg. In the separating calorimeter part of the liquid, say M1 kg will be separated from the wet steam. Hence the dryness fraction of the wet steam will increase to x1 (state B) which will pass through the throttling process valve. After the throttling process the steam in the throttling International Journal of Research in Engineering and Applied Sciences (IJREAS)© IJREAS, Vol. 02, Issue 01, Jan 2014ISSN : 2249-9210  42 calorimeter will be in superheated state (state C).It consist a narrow throat (Orifice). Steam Pressure and temperature are measured by pressure gauge and thermometer. The steam after throttling process passes through the heat exchanger and condensate is collected. Steam Generator is also provided to supply the saturated steam (Max) at 5 kg/cm² pressure[3].  Fig. 1 - Schematic diagram for the separating and throttling Calorimeter   Fig. 2 - T-S diagram of the separating and throttling calorimeter  From the steady flow energy equation; Q – W = hC - hBSince throttling takes place over a very small distance, the heat transfer is negligible, i.e., Q = 0. Then the steady flow energy equation for the throttling process becomes, hC = hBHence, enthalpy after throttling = enthalpy before throttlinghC = hf1 + x1 hfg1If the pressure of the steam before throttling, the pressure and temperature of the steam after throttling, are known the value of x1 can be calculated using steam tables.Using the average values, obtain the specific enthalpy of steam at (state C) hence calculate the dryness fraction of incoming steam. Also calculate the specific enthalpy of incoming steam. 3. Principle of working “Chemical energy in the fuel is released in the form of heat during combustion. The products of combustion, the flue gases, transfer this heat to the coil carrying water by radiation and convection. Residual heat in the flue gases is absorbed in the economizer, where feed water is heated to expel dissolved gases. Air is supplied for the combustion by the blower which imparts velocity and pressure to the air by its centrifugal action of its rotating blades. For maximum efficiency correct amount of air has to be supplied. More air than necessary results in wastage of heat because of a larger quantity of hot gases escaping from the chimney”. “Lesser air results in incomplete combustion and soot formation. Soot gets deposited on heat transfer surfaces. To use minimum  possible excess air requires vigorous mixing of air and fuel, so that air is available to each fuel particle. Before the fuel can burn, it has to evaporate into gaseous form. To achieve this, it is atomized into a fine mist by passing it through swirler in the nozzle under pressure. Atomization produces very large surface area from which fuel can evaporate. Fuel cannot be properly atomized if it is too viscous. Light Diesel Oil (LDO) has a low viscosity so that it can be easily atomized, except in very cold wheather. Furnace oil (FO) or low sulfur heavy stocks (LSHS) are too viscous at room temperature and have to be heated to reduce their viscosity”[1].In the operation of the boiler it is of primary importance to have water in the proper condition.  Make sure that the boiler feed water is soft. If the water is not soft, regenerate the water softener.  To ensure that the water behaves as a proper cooling medium. It is essential to see that  The water continuously wets the heating surface.  The water does not corrode the heating surfaces.  The water does not erode the heating surfaces.  The water has necessary chemicals within it such that a  protective oxide layer is formed on the surfaces. 4. Experimental procedure “The trials were conducted on Thermax diesel fired water tube Boiler (Three pass Reverse Flue coil type steam generator) coupled with Separating & Throttling Calorimeter set up to evaluate the performance of system. The performances  parameters were compared with Separating & Throttling Calorimeter and without Separating & Throttling Calorimeter for same boiler output conditions. Known quantity of steam is circulated into the Separating & Throttling Calorimeter. and is controlled with valve manually . The dry steam comes out at very high temperature and pressure. It is pulsating in nature. The experimental Separating & Throttling Calorimeter set up is shown in figure (2). Several components of this set up have been designed and fabricated”.  International Journal of Research in Engineering and Applied Sciences (IJREAS)© IJREAS, Vol. 02, Issue 01, Jan 2014ISSN : 2249-9210  43 “A cylinder is designed and fabricated to collect the high temperature & pressure steam. Gate valve is used to control the flow of steam. Valves are used to control the inlet and outlet steam supply from the boiler and water from main tank. Digital Temperature Indicator is used to measure the temperature of steam. A Bourdon's pressure gauge is used to measure the  pressure and it is mounted on control panel. Digital control panel is provided to acquire data such as blower down, steam temperature, steam pressure, water level, fill-off-fire and control. Temperature gauges are provided at the intake, exhaust manifold and other test points along the boiler route.Rota meter is used to measure the steam flow rate in litre per hour (LPH) The following procedure adopted for the experimentation on separating and throttling calorimeter. 1.Start the boiler and supply steam to the separating and throttling calorimeter unit.2.Start the cooling water flow through the condenser.3.Open steam valve and allow the steam to flow through the calorimeters to warm through the steam.4.Open the throttle valve and adjust to give a pressure at exhaust of about 5cm Hg measured on the manometer.5.Drain the separating calorimeter.6.Start the test and take readings at 2-3 minutes intervals. 7.When a reasonable quantity of condensate is collected measure the quantity of separated water and the quantity of condensate. 5. Performance parameters of boiler 5.1 Evaporative capacity The evaporative capacity of a boiler may be expressed in terms of:(i) Kg of steam/h (ii) Kg of steam/h/m2 of heating surface(iii) Kg of steam /Kg of fuel fired. 5.2 Equivalent evaporation It is defined as the amount of water evaporated from water at 1000 C to dry and saturated steam at 1000 C. It is denoted by symbol mem = e m (h – h) af   2257. 5.3 Factor of evaporation It is defined as the ratio of heat received by 1 Kg of water under working conditions to that received by 1 Kg of water evaporated from and at 1000 C. It is denoted by Fe = (h – h) f   2257 5.4 Boiler efficiency It is the ratio of heat actually utilized in generation of steam to the heat supplied by the fuel in the same period. It  is denoted by symbol çç =m ( h – h) af  C.V.Where ma – Mass of water actually evaporated into steam per Kg of fuel at the working pressureh – Enthalpy of steamhf - Enthalpy of feed water temperature in KJ/KgC.V. – calorific value of the fuel in KJ/Kg. 5.5 Dryness fraction of steam Dryness Fraction = Mass of dry steam Mass of mixture Therefore, X = MMM 2121 x    Where,M1 is the Quantity of Separated water. (in Kg)M2 is the mass of condensate. (in Kg)P1 is the steam pressure before throttling in bar P2 is the Steam pressure after throttling in bar T1 is the steam temperature before throttling in 0CT2 is the steam temperature after throttling in 0CPa is atmospheric pressure in bar measured using aneroid  barometer. Alternate Method It is related with wet steam. It is defined as the ratio of the mass of actual dry steam to the mass of steam containing it. It is usually expressed by the symbol ‘X’ Let X 1  = Dryness fraction of steam considering Separating calorimeter X 2 = Dryness fraction of steam entering the Throttling calorimeter  Now, the actual dryness fraction of steam in the steam main, X = X 1  * X 2   wss1 MMMx   Where: M S = mass of dry steam (Kg) M w  = mass of water separated out (Kg) Thus if in 1 Kg of wet steam 0.9 Kg is the dry steam and 0.1 Kg water particles then X = 0.9 No steam can be completely dry and saturated, so long as it is in contact with the water from which it is being formed [1] .  satsup p2g1fg21f  ttChhxh     International Journal of Research in Engineering and Applied Sciences (IJREAS)© IJREAS, Vol. 02, Issue 01, Jan 2014ISSN : 2249-9210  446. Specifications and Observations Table 1 - Specifications of Test Set up MAKE REVOMAX   Type Three Pass Reverse Flue   Coil type Steam Generator    Steam output at 100 0 C   200 kg/hr LDO   Heat output   451.44 MJ/Hr    Steam pressure and temperature   10.5 bar , 185 0 C   Efficiency   @88%   Fuel Consumption   12 kg/hr, C.V.=   42.7 MJ/kg   Boiler heating surface area   3.5 m²   Economizer heating surface area   0.9 m²   Electric Supply   415 volt, 50 Hz , 3 phase   Blower motor (3000 rpm)   735 W , 1 H.P.   Water Pump (100 rpm)   550 W, 0.75 H.P   Total connected load   1.9 KW   Softener (Maxi. Working Pressure)   3.5 Kg/cm 2   The following observations recorded during experimentations. Table 2 - Observations from Boiler control panel  Sr.  No. Steam Pressure P 1 in bars Steam Temperatur e in 0 C Exhaust gas Temperature 0 C Fuel Pressure in Kg/cm 2  1. 1.5 105 150 2.1 2. 2.5 115 165 2.3 3. 3.6 120 180 2.5 4. 4.3 137 195 3.0 5 5.2 150 258 3.3 6. 6.5 160 310 3.5 7. 8.0 180 336 3.6 Table 3 - Observations from separating and throttling calorimeter Test set up P 1   in  bar    P 2   in  bar    T 1   in 0 C   T 2   in   0 C   M 1   (kg)   M 2 (kg)   P a in  bar    Manometer reading in cm of Hg 1.5   1.2   101   90   10   7   0.98   5   2.5   2.0   105   95   10   7   0.98   5   3.6   3.1   112   100   10   7   0.98   5   4.3   3.5   125   112   10   7   0.98   5   5.2   4.5   135   120   10   7   0.97   5   6.5   5.2   148   132   10   7   0.97   5   8.0   6.5   169   140   10   7   0.98   5    Fig. 2.-Typical T-S diagram for steam 7. Result & Discussions If the steam whose dryness fraction is to be determined is very wet then throttling to atmospheric pressure is not sufficient to ensure superheated steam at exit. In this case it is necessary to dry the steam partially, before throttling. This is done by passing the part of steam from the steam main through separating calorimeter as shown in figure. The steam is made to change direction suddenly, and the water, being denser than the dry steam is separated out is measured at the separator, the steam remaining, which now has dryness fraction, is passed through the throttling calorimeter. With the combined separating and throttling calorimeter it is necessary to condense the steam after throttling and measure the amount of condensate (Ms). It was observed that with increasing the boiler steam pressure there is increase in steam temperature and when the part of the steam enters into the separating calorimeter steam pressure  before throttling is higher than steam pressure after throttling. It is also observed that steam pressure decreases after throttling. Corresponds to the steam pressure after throttling, from steam table it was noted that steam temperature measured is greater than the saturation temperature. Therefore the steam becomes superheated steam. From the measured values the various  parameters like dryness fraction of steam, enthalpy of superheated steam, equivalent evaporation and factor of evaporation and boiler efficiency calculated. 8. Conclusion Performance analysis on separating & throttling calorimeter was carried out. The following parameters were measured: Steam Temperature, Steam Pressure, Exhaust Gas Temperature, Fuel Pressure, and Water Temperature after Economizer at various conditions. Dryness fraction of steam was calculated. The following conclusions were drawn under various parameters like boiler steam temperature; boiler steam pressure; steam  pressure before throttling; Steam pressure after throttling; steam temperature after throttling; steam flow rate measured. Water  particles from wet steam can fully separated, thus resulting in  precise value. The actual Dryness fraction of steam calculated. Boiler efficiency improved by 10 %.  International Journal of Research in Engineering and Applied Sciences (IJREAS)© IJREAS, Vol. 02, Issue 01, Jan 2014ISSN : 2249-9210
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