12th International Symposium on District Heating and Cooling

The <strong>12th</strong> <strong>International</strong> <strong>Symposium</strong> on District Heating and Cooling,September 5 th to September 7 th , 2010, Tallinn, Estoniaconcept is possible within the operational limits of theCHP plant.In the following, first the used multiperiod load model isdescribed. Further a brief introduction to biomass fastpyrolysis is given and it is shown how the process hasbeen simulated and integrated. Then the modification ofthe European standards is explained, results arepresented and finally restrictions of the work andoptions for further improvement are discussed.District Heat Load [MW]252015105Heat Duration Curve - Multiperiod ModelIntegrated Case - Lower LoadsDISTRICT HEATING LOADThe CHP plant chosen has been integrated into a virtualDHN. Therefore yearly data of a real DHN has beenscaled so that the CHP plant provides 60% of the hourlypeak demand of the DHN when on full load. The CHPplant is assumed to be shut off at 50% load whichcorresponds with 30% demand in the DHN. As stated in[4], those are common operating parameters forcommunal solid fuel-fired CHP plants.In order to represent the yearly production of the basecase plant a multiperiod load model was developed.One full load and five part load levels have been chosento represent the heat duration curve. The pyrolysisintegrated CHP plant is represented by 7 part loadlevels since lower DH loads can be supplied, asexplained later. Operating time periods per part loadlevel are set of equal length and -together with the fullload period- match the total operation hours and yearlyDH generation of 94.5 GWh as shown in figures 1a and1b. For each load level, fuel input and pyrolysis yield arethen iterated matching the required DH output. DHdemand not provided by the CHP plant is assumed tobe generated in oil-fired heat-only boilers with a thermalefficiency of 0.85District Heat Load [MW]252015105Heat Duration Curve - Multiperiod ModelBase Case00 50 100 150 200 250 300 350District Heat LoadMultiperiod Model DH LoadTime [d]Real CHP DH LoadFig. 1a: DH Load Multiperiod Model - Base Case00 50 100 150 200 250 300 350District Heat LoadMultiperiod Model DH LoadTime [d]Real CHP DH LoadFig. 1b: DH Load Multiperiod Model – Integrated CaseCHP PLANT INTEGRATED WITH WOOD PYROLYISWood Pyrolysis ModelBiomass fast pyrolysis is the thermal conversion ofbiomass in the absence of oxygen at temperatures ofapproximately 500 °C and pressures close toatmospheric [5]. The basic idea of the pyrolysis unit isderived from the bioliq® process developed by theForschungszentrum Karlsruhe (FZK). There, fastpyrolysis is applied in order to yield a high share ofliquid pyrolysis product. Biomass is indirectly heatedand pyrolysed with sand in an inert atmosphere at atemperature of about 500 °C. Subsequently, thepyrolysis gases are condensed and the liquid fraction(also referred to as wood oil) is mixed with the coke andforms the so-called bioslurry which leaves the plant asthe final product. In this work we use data published byFZK [6] and hence assume that 90% of the biomass‘energy is converted into bioslurry whereas 10% accruesin gaseous form. The pyrolysis gas is thought to be cofiredin the boiler and hence its energy is subtractedfrom the fuel input into the boiler.As pyrolysis requires a low fuel moisture content ofapproximately 10% [5] a dryer must be integrated aswell. Indirect steam drying is applied, since this alsoallows the regulation of the DH load. As explained later,regulation is necessary since the enthalpy of the steamflow after the modification exceeds the demand of theDHN and hence must be adjusted.The wood pyrolysis process is modelled as follows: Theheat of pyrolysis of wood is set to 1.87 MJ/kg (moisturecontent 10%) using data for pine derived from [7].Therewith the pyrolysis yield is calculated from the heatextracted from the flue gases.CHP Plant – Base CaseA base case CHP plant with a bubbling fluidized bedboiler (shown in fig. 1) has been simulated in full and169