The presented software is based on the new theoretical findings on heat transfer in boilers and delivers a proven +/-2% uncertainty, an unique feature. It can be applied to carry out tasks like these:
HEAT TRANSFER ANALYSIS
HEAT TRANSFER ANALYSIS IN CASE OF FIRING TWO FUELS AS FOUND IN COAL POWER PLANTS COFIRING BIOMASS OR WASTE DERIVED FUEL (RDF).
There is no limitation in boiler size, which is especially convenient in case of water tube boilers (also called utility or power boilers). Equations for radiant heat transfer from CO2 and H2O vapor in flue gases are not numerical but physical ones, which assures the highest possible accuracy unlike in case of numerical equations where there are cases with up to 300%(!) discrepancy (see Underlying theory tag for more explanation).
The software is extremely simple to use and skilled boiler designer gets along with it in a single go. A great care has been taken to make it simple and straightforward and the examples given (see side menu) are in essence instructions for the user.
The software calculates a heat transfer in fossil fuel (oil, gas, biomass, waste derived fuel) fired fire-tube and water-tube steam, hot water and waste heat boilers of arbitrary geometry operated at arbitrary operating conditions with pressure up to 100bar/1450psi (higher pressure can be added). Based on new theoretical findings, the extensive testing and verification work the software delivers most accurate results to date and is therefore hoped to become a welcome and trusted boiler designer's companion.
The software can also handle a boiler fired with two fuels at same time! This is especially convenient in the case of coal fired power plant boiler, which cofires a biomass or waste derived fuel (RDF).
All a boiler designer has to be careful of is to enter the physically correct data for the software is just a tool and as such can not know that, for instance, 2MW boiler with 10 tubes can not be calculated as the software will try to "squeeze" all gases into them generating a run time error as either the validity range of the equations will be exceeded or an extremely high static pressure drop will result no burner can cope with (or to run it with just 10l/h of fuel, which will produce run time error as gases will be "mathematically" cooled down to subzero as software tries to extract the heat from them that is not there etc.). Also when there are too many fins on an economizer tubes results in a run-time error because the economizer would theoretically be able to transfer more heat than it is available in flue gases. In such cases an alert is issued that exit flue gas temperature is too low and program execution is redirected to the particular geometry data input section.
A boiler can consist of multiple segments such as furnace, channels and tubes, with or without front or/and rear cooled door. The boiler segments can be combined, which makes calculation of next to every known boiler design possible (with exception of few special cases for which dedicated proprietary procedures were developed). A part list of boiler designs the software can handle is shown here.
Following water-tube boiler designs are incorporated:
furnace (circular or rectangular, horizontal or vertical)
furnace and 1,2 and 3 channels following it (in this case rectangular channels are assumed), horizontal or vertical
tube-array superheater in furnace or in channel after it
tube-array evaporator in channel after furnace or/and in 2nd channel after furnace
coiled tube with 2 ring slots (thermal oil heater).
Following fire-tube boiler designs are incorporated:
with or without fins (used in some domestic hot water and also in cast iron boilers)
wetback or dryback (with or without cooled furnace bottom)
with or without internal reversing chamber (found in 3-and 4 pass boilers)
with or without cooled front door
with or without fire-proof steel cylinder (used in some domestic size hot water boilers).
3. Channel after furnace (if any):
one or more
circular or rectangular
horizontal or vertical
with or without fins fins
with or without baffles (inserts blocking the flue gas path resulting in an intensified heat transfer, common in cast iron boilers).
4. Boiler with 1, 2 or 3 tube assemblies after furnace (2-pass, 2-pass reverse flue, 3- pass, 4-pass):
horizontal or vertical
tubes can have coiled-wire turbulators/turbilence promoters or dents.
5. Boiler with cooled rear door (circular shape is assumed).
7. Waste heat (exhaust gas) boiler such as hybrid biomass systems without or with supplemental firing in various configurations as per above.
8. Tube-array or tubular (boiler like) economizer.
Boiler material is assumed steel.
Economizer tubes can be made of following materials:
Boiler liquid can be following (more can be added as needed):
Rankine cycle liquid
Input and output values can be either in Metric or English units.
Order of calculations
1. A stoichiometry of combustion, adiabatic combustion temperature, flue gas enthalpy at that temperature, and a first estimation for the furnace exit temperature are calculated.
2. Convective and radiant heat transfer are considered to be simultaneously coexistent. For convection, the relevant temperature is mean logarithmic, for radiation the mean radiant temperature, MRT (the latter is calculated by a newly developed equation as explained in Underyling theory tab.
3. The impact of the turbulators, tube dents or baffles is taken into account according to the proprietary developed procedure.
4. The convective and radiant parts of the heat transfer in the furnace are summed-up and deducted from the flue gas enthalpy at the adiabatic combustion temperature. The result is a temperature at the furnace exit.
5. The calculated flue-gas exit temperature is compared to the estimated one in step 1. If they do not meet the preset difference (0.1°C) a new estimation is calculated as the average of assumed one in step 1 and the calculated one. The procedure is then repeated.
6. This same procedure is applied to every boiler segment using the exit temperature of flue gas from one segment as the initial temperature in the next section. Thus, the initial temperature in next boiler section is equal to the exit temperature from preceding section.
7. The sum of the heat transferred in all boiler sections represents its heat output which, when divided by heat released from fuel, gives a boiler efficiency.
Discrepancy sources between measured and calculated values
There are always differences between calculated and actual values. The discrepancies are of an operational (fouling, scaling on gas and water side) and of mathematical nature (heat transfer equations are always derived from experiments). In general, for new and well maintained boilers the discrepancy to actual values is between 1-2% (boiler output, steam capacity) being unique.
Impact of fouling, soot and scale deposits
The impact of fouling and soot deposits on gas side as well scale deposits on the water side have deliberately NOT been included. The reason is that this is always coupled with an increased calculation uncertainty. Every boiler starts its life with the commissioning process where it has to deliver the claimed performance. Over time boiler performance becomes affected by fouling, soot and scale deposits. The magnitude depends on fuel, operating conditions etc., which can not be predicted and taken in account accurately enough. Hence, what a boiler displays during commissioning process counts, which is what this software delivers.
Boilers which cool down the flue gases below the water dew point are called condensing boilers. In best case the condensation rate will reach 40%. In case of gaseous fuel this would correspond to a maximum 4-5 percentage points efficiency increase (half of that in case of solid and liquid fuels). Since the condensation rate can not be accurately predicted, maximum efficiency increase is known and condensing boilers are of the proprietary designs, those boilers are not covered with this software. When the water dew point in flue gases is reached the software issues an alert about the impending condensation, though.
BOILER DESIGN SOFTWARE FOR FIRE-TUBE & WATER-TUBE BOILERS