Integrating sludge drying in biomass fueled CHP plants
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ORIGINAL ARTICLE
Integrating sludge drying in biomass fueled CHP plants Jinshan Wang1,2 • Chaudhary Awais Salman1 • Bin Wang2 • Hailong Li1 Eva Thorin1 1 2
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School of Business, Society and Engineering, Ma¨lardalen University, 72123 Va¨stera˚s, Sweden Key Laboratory of Refrigeration Technology of Tianjin, Tianjin University of Commerce, Tianjin 300134, China
Received: 26 June 2020 / Revised: 23 August 2020 / Accepted: 29 August 2020 Ó The Author(s) 2020
Abstract Handling sludge through thermal conversion is environmentally friendly, which, however, requires sludge drying. This work proposed to use the waste heat of flue gas (FG) to dry sludge. The integration of sludge drying in biomass fueled combined heat and power (CHP) plants can clearly affect the performance of downstream processes in FG cleaning, such as flue gas quench (FGQ) and flue gas condenser, and further affect the energy efficiency of CHP. In order to understand the influence, a mathematical model and an Aspen PLUS model were developed to simulate the drying process and the CHP, respectively. Based on simulations, it is found that the increase of feeding rate of sludge and the moisture content of sludge after drying can decrease the water evaporation in FGQ. An increase in the feeding rate of sludge in combination with a drop of moisture content of sludge after drying can decrease the heat recovery from FG. When using dried sludge to replace biomass, the amount of saving could be influenced by the moisture content after drying and the flow rate of sludge. Simulation results show that drying sludge to a moisture content of 40% leads to the maximum biomass saving.
Cd cFG cPG cpv cpw d dUsludge
Keywords Flue gas quench Heat recovery Sludge drying CHP Energy efficiency List of symbols A1 Contact area between the sludge and the heated wall (m2) A2 Heat dissipation area of sludge (m2) Aw Area of heat and mass transfer per unit time in FGQ (m2/s)
MH2 O Mair mDS md mFG mv PT PV PV,S(Ts)
& Hailong Li [email protected]
Qcv Qin
G g DH h hbw hc hm hrad hws
Drag force coefficient Specific heat of FG (J/kg K) Specific heat of air (J/kg K) Specific heat of water vapor (J/kg K) Specific heat of liquid water (J/kg K) Diameter of droplets (m) Heat used to change the temperature of sludge bed (J) Flow rate of dry FG (kg/s) Acceleration of gravity (m/s2) Latent heat of vaporization in the surface water of sludge (J/kg) Coefficient of heat transfer in FGQ (W/m2 K) Heat transfer coefficient of static sludge (W/ m2 K) Coefficient of convective heat transfer in the surface of sludge (W/m2 K) Coefficient of mass transfer in FGQ (W/m2 K) Coefficient of radiant heat transfer in the surface of sludge (W/m2 K) Complex coefficient of heat transfer between FG and sludge (W/m2 K) Mole mass of water (g/mol) Mole mass of air (g/mol) Mass of dry sludge (kg) Mass of water droplets (kg) Mass flow rate of FG (kg/s) Drying rate (kg/m2 s) Total pressure (Pa) Partial vapor pressure of sweeping air (Pa) Partial vapor pressure of the surface of sludge (Pa) Released heat of
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