It is also an editable graphic with text…. This diagram is a top and bottom zigzag arrangement design. This has a visual effect by balancing the chevron arrows and circles. It's also an editable graphic with text and icon….
This diagram is a LEGO block design that gradually increases in height one step at a time. This is used to indicate evolution, growth, and sequential growth.
It is also an editable…. This diagram is an iceberg silhouette design. Four segmented icebergs represent the progress or flow of work. It's also an editable graphic with text and icon placeholders. This diagram is a list of placemarks. This allows you to create 4 sub-lists in order. It is also an editable graphic with text and icon placeholders.
Search Keywords: PowerPoint,…. This diagram is a design with two arrows facing each other. This can summarize different concepts as opposed to each other. This diagram is an arrow banner design that hits the center of an archery target. This explains the five information cycles and the results. It is also an editable graphic with…. Knowing the pressure and the temperature, the specific enthalpy after the evaporator can be defined. The pressure before the economizer can be calculated by adding the pressure loss in the economizer to the feedwater pressure after economizer.
The feedwater temperature might be stated in the boiler design assignment. The mass flow rate before the economizer is the blowdown mass flow rate added to the mass flow rate from the steam drum to the superheaters.
The steam goes through a high- pressure turbine before it enters the reheater. In the high-pressure turbine, the specific enthalpy of steam decreases according to the isentropic efficiency of the turbine.
Isentropic efficiency is normally between 0,8 and 0,9. A part of the low-pressure steam coming from high-pressure turbine continues to the high-pressure feedwater heater closed-type feedwater heater.
I II III Heat load Superheating is often applied in three stages having spray water groups between each other Figure 9: An example of the heat load share of to reduce steam temperature when necessary.
Between reheaters, the steam temperature is controlled using other means. Spray water originates normally from the feedwater line before the economizer. Thus the pressure difference is the pressure loss of the heat transfer surfaces between the economizer inlet and the location of the spray water nozzle.
An example of a possible heat load share between the superheater stages is shown in figure 9. Pressure loss in superheaters can be divided into equal partial pressure losses corresponding to each superheater stage.
Pressure loss of the spray nozzles can be neglected. Temperature rise over all superheaters can be divided into quite similar parts along the same principle.
Spray water group mass flow Normally the mass flow rate of superheated steam live steam is known. Thus, mass flow rate calculations start usually by calculating the mass flow rate of spray water to the last spray water group which is in this example between the second and third superheater stages. The mass flow rates can be solved with energy and mass balance equations. With the equations below equation 1 , the mass flow rate of steam after second superheater stage and mass flow rate of spray water to the last spray water group can be calculated.
Figure 10 shows a flow chart with the symbols visualized of the boiler arrangement used in this calculation model. Calculations of heat load When the steam parameters and mass flows have been determined, the heat load of the heat exchanger units can be calculated. The heat load is the heat transferred by a heat exchanger calculated in kW. This calculation example is based on three stage superheating.
Air preheater In order to calculate the heat load for the air preheater, we need to know the combustion air mass flow, the temperature of the flue gases and the incoming air. The combustion air fed into air preheater, is taken from upper part of the boiler room. Determination of boiler efficiency Standards There are two main standards used for definition of boiler efficiency.
However, this chapter calculates the efficiency according to the DIN standard. Major heat losses Heat loss with unburned combustible gases The typical unburned combustible gases are carbon monoxide CO and hydrogen H2.
In large boilers usually only carbon monoxide can be found in significant amounts in flue gases. If a relevant amount of some other flue gas compound can be found in the flue gases, it should be added to the equation.
Heat loss due to unburned solid fuel Unburned fuel can exit the furnace as well as bottom ash or fly ash. The heating value of ashes can be measured in a specific laboratory test. Some estimates of the losses with unburned solid fuels are presented in table 1: Table 1: Estimates of losses with unburned solid fuel.
To decrease flue gas losses, flue gas exit temperature should be decreased. Heat loss due to wasted heat in ashes Ash can exit the furnace either as bottom ash from bottom of the furnace or as fly ash with flue gases. The loss of sensible heat of ash is therefore of great importance in recovery boilers.
Another possibility to determine the heat transfer losses to the environment is to use a table from the DIN standard, presented in table 2. Table 2: Estimations of heat transfer losses by radiation. This lowers the boiler efficiency. In addition, steam is sometimes also used to atomize fuel in the burners. Internal power consumption The power plant itself consumes a part of the electricity produced. Since the power used is electrical and taken from the grid , the internal power consumption share is reduced from the final boiler efficiency in boiler calculations.
Calculating boiler efficiency There are two different means of calculating the boiler efficiency: The direct method and the indirect method. The indirect method provides a better understanding of the effect of individual losses on the boiler efficiency. DIN Unit By Krishna Mohan.
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