Heat balance calculation steam

An interesting application of this approach in another field has been described by Keller (K2). In the design of steam turbines rather complicated heat-balance calculations are required. While each particular installation is different, and therefore requires a different mathematical model, the components of each turbine are always similar. A large-scale computer program was developed, therefore, which would through suitable instructions combine the calculations required for each component into an over-all heat balance for the turbine. 

Investigations in connection with proposed topping units may cover various aspects, for instance, determination of additional capacity obtainable with assumed initial steam conditions or, conversely, selection of initial steam conditions for a desired increase in power. Incidentally, the improvement in station heat rate is also calculated for use in evaluating the return on the proposed investment. However, this evaluation involves heat-balance calculations for the complete plant including the feed-heating Q cle adjusted to the new conditions. 

Often in plant operations condensate at high pressures are let down to lower pressures. In such situations some low-pressure flash steam is produced, and the low-pressure condensate is either sent to a power plant or is cascaded to a lower pressure level. The following analysis solves the mass and heat balances that describe such a system, and can be used as an approximate calculation procedure. Refer to Figure 2 for a simplified view of the system and the basis for developing the mass and energy balances. We consider the condensate to be at pressure Pj and temperature tj, from whence it is let down to pressure 2. The saturation temperature at pressure Pj is tj. The vapor flow is defined as V Ibs/hr, and the condensate quality is defined as L Ibs/hr. The mass balance derived from Figure 2 is ... 

Finally, we have been sloppy in associating the flow rate of steam with the heating coil temperature. The proper analysis that includes a heat balance of the heating medium is in the Review Problems. To side step the actual calculations, we have to make a few more assumptions for the valve gain to illustrate what we need to do in reality ... 

Thus, in this example, assumption of the deaeration steam allows the steam balance to be closed. However, this is based on an assumed deaerator flow. The actual flow to the deaerator can be calculated from a heat balance around the deaerator. Figure 23.23 shows the flows into and out of the deaerator. If the boiler feedwater flow and condensate flows are known, together with an assumed value of the vent steam, then the flowrate of deaeration steam can be calculated from an energy balance. 

The heat of combustion in a process heater or steam boiler may liberate 100 X 106 Btu/h. If the heater s efficiency is 78 percent, the heat absorbed by the tubes should be 78 X 106 Btu/h. When observing a heater s operation, it is a good idea to check this heat balance by calculation. 

Detailed analyses of the major flows and temperatures have been utilized to make heat balances for a number of tests. The heat balance can, in turn, be used to calculate a heat transfer efficiency for the production of steam, by either an input-output method or a heat loss method. The... 

Similar results, heat balances plus calculated efficiencies, are given in Table VI for seven additional tests. Results from LSF-31 are included for comparison. The results for all eight tests are considered satisfactory based on the error analysis mentioned above. For those tests where the enthalpy balance closes within + 2.556, either method for calculating efficiency may be used for the other four tests, the heat loss method value should be selected. Thermal performance of the unit — the steam generating capacity compared to the Btu input — appears to be similar for all eight tests. 

After the first screening step, based on preliminary heat balances and engineering judgement, six systems were selected. In the calculations, it was assumed to have year-round production in the BIG-GT plant, cane trash would be mixed with bagasse and any steam in excess of the mill need would be used in a new condensing backpressure nirbogenerator at the appropriate pressure level. The results are shown in Table 3. 

Steam undergoes a Carnot cycle between temperatures 500 °C and 300 °C. During the isothermal heating step, the steam expands from pressure 50 bar to 30 bar. Determine the states in each of the four corners A, B, C, and D of the cycle (see Figure 4-f ). calculate the thermodynamic energy balances and determine the thermodynamic efficiency of the cycle. 

The economic advantages of a multiple-effect evaporation resulting from better steam utilization are reduced to a certain extent by additional costs due to (a) pressure gradient over the series of evaporators, which is necessary to maintain the reasonable temperature difference between steam and boiling solution in a sequence of evaporators, and (b) larger heat transfer surface area necessary to maintain a technically justified evaporation rate. Therefore, the design of a particular evaporation system should be based on economic-balance calculations. 

An important point to be discussed with regard to chemical desorption is the question of the required steam rate. The steam injected into the regeneration unit serves two purposes it provj des the sensible and latent heat required for the desorption oper tion, and it represents the diluent gas needed to keep the partial pressure of acid gas in the gas phase low enough to allow strippiiig to take place. Consequently, the required steam rate may be dict ted either by the heat balance, or by stripping operation. The minimum steam rate needs to be calculated for both requirements, and the actual minimum is the larger one of the two. 

Feedwater system malfunctions causing a reduction in feedwater temperature were not modelled as described above rather, the transient was analysed by calculating conditions at the feedwater pump inlet following the removal of a low-pressure feedwater heater train from service. The feedwater conditions were then used to recalculate a heat balance through the high-pressure heaters. This heat balance gives the new feedwater conditions at the steam generator inlet. The decrease in feedwater temperature transient so calculated was less severe than (and therefore... 

The stripping zone model performs heat, mass and pressure balance calculations around the stripping zone. A tunable stripping efficiency curve is included. The stripping efficiency is related to the ratio of catalyst flow to stripping-steam flow. 

Heat balances are determined for all the reactor models discussed. Therefore the heat duties of the radiant tubes, convection section heaters, waste heat boilers, and assoeiated steam drums are all explicitly calculated and reported. Heat losses are part of the models, as described in the Heat Losses section. The enthalpies of all the streams entering and leaving each piece of equipment are caleulated and reported. These streams include, for example, the process, fuel, air, and flue gas. Combustion, and all reaction related heat effects, are handled in models using enthalpies of all species including heats of formation based on of the elements at their standard states, so heats of reaction are avoided. 

The measured fuel flows, arch oxygen composition, and high pressure steam drum heat balance confirm that the heat duties calculated from the process side (as opposed to the flue gas side) are most accurate, as would be expected. The high pressure steam system and boiler feed water measurements impact significantly on the convection section heat balance since boiler feed water preheat and steam superheat duties make up the majority of the convection section duty. The high pressure steam import flow, and the expected versus measured and calculated S5mthesis gas compressor steam turbine performance further support that the process side, and not the flue gas side measurements are the most accurate. 

The outlet methane concentration bias in the objective function was heavily weighted (to drive it toward zero, since the objective function is the sum of the weighted squares biases) and therefore explains the good agreement between calculated and observed values. The process air flow measurement bias (difference between measured and calculated) was a parameter, so the calculated nitrogen composition is precisely equal to the measured value. The air flow measurement bias was 4.4% of the measured value at the solution. The calculated outlet temperature is surprisingly close to the measured value. The heat balance around the high pressure steam drum required only a 1.2% heat loss to close in this case. That balance is of course affected by numerous other measurements, so the calculated secondary reformer outlet enthalpy can only be said to be part of the overall consistent set of information. 

Some of the new signals mentioned above permit many economic variables to be generated. For example, the conversion in a reactor can be assimilated from a heat balance across it. Yield can be calculated as the ratio of feed and product composition. The efficiency of a steam plant is similarly the ratio of thermal power to the heat content of the flowing fuel. The cost of operating a separation unit can be determined from the mass flow rates of utilities and products and the measurements of product quality. 

The most easily understood demonstration of feedforward is in the control of a heat exchango. The computation is a heat balance, where the correct supply of heat is calculated to match the measured load. The process is pictured in Fig. 8.3. Steam flow W, is to be manipulated to heat a variable flow of process fluid Wp fixm inlet temperature T to the desired outlet temperature Ti. 

Calculate the reflux heat, at Tray Dl. Reflux heat is defined as the apparent heat imbalance between external heat quantities at the point in question in the tower. These external heat quantities are denoted as Q with appropriate subscripts to signify their location. External heat input quantities are defined as the heat contained in the feed plus all heat to the system at product strippers either directly as steam or indirectly throu reboilers. External heat output quantities at a given tray are defined as the heat contained in liquid products leaving the system from points lower in the towier, the heat contained in the internal vapors of products plus steam and the heat contained by a product liquid flowing to the sidestream stripper. If the tray is nbt a sidestream draw tray, this latter quantity does not enter into the heat balance. 

Set the steam rate to the tower bottoms at 10 pounds per barrel of bottoms product. In the case of catalytic towers and unlike crude unit towers, it is not necessary to set up a material balance around the feed entry point and the bottoms stripping trays because the vapor-liquid traffic at this point does not influence the overall heat and material balance calculations. 

Data on the heats of reaction of amines with the acid gases are necessary for the generation of individual tray and overall vessel heat balances for the absorber and stripper, the calculation of the amount of steam needed in the reboiler, and the estimation of heat duties of heat exchange equipment in the plant. As noted previously, the heats of reaction are not constants for each amine and acid gas, but generally decrease as the acid gas concentration in... 

An example of the heat balance diagram and corresponding T-S chart of the Super LWR steam cycle are depicted in Fig. 3.9 [3]. According to the engineering thermodynamic knowledge, the thermal efficiency of the Super LWR steam cycle depicted in Fig. 3.10 [3] can be finally calculated by (3.1). 

The cycle efficiency may be calculated using a method similar to that already mentioned, but in connection with this Qrcle it is customary to design a flow diagram and to prepare a complete heat balance of the plant. In small and medium-sized plants, one or two extraction heaters may be used in addition to the exhaust heater that serves the steam-driven auxiliaries, and in large plants up to seven heaters may be employed. 

Thermocompression Evaporators Thermocompression-evap-orator calculations [Pridgeon, Chem. Metall. Eng., 28, 1109 (1923) Peter, Chimin Switzerland), 3, II4 (1949) Petzold, Chem. Ing. Tech., 22, 147 (1950) and Weimer, Dolf, and Austin, Chem. Eng. Prog., 76(11), 78 (1980)] are much the same as single-effect calculations with the added comphcation that the heat suppied to the evaporator from compressed vapor and other sources must exactly balance the heat requirements. Some knowledge of compressor efficiency is also required. Large axial-flow machines on the order of 236-mVs (500,000-ftVmin) capacity may have efficiencies of 80 to 85 percent. Efficiency drops to about 75 percent for a I4-mVs (30,000-ftVmin) centrifugal compressor. Steam-jet compressors have thermodynamic efficiencies on the order of only 25 to 30 percent. 

Flash Evaporators The calculation of a heat and material balance on a flash evaporator is relatively easy once it is understood that the temperature rise in each heater and temperature drop in each flasher must all be substantially equal. The steam economy E, kg evap-oration/kg of I055-kJ steam (Ib/lb of lOOO-Btu steam) may be approximated from... 

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