Gasifier Feedstock Hydrokinetics

Transcription

1 Gasifier Feedstock Hydrokinetics A SUNY Cobleskill Initiative Douglas Goodale, Ph.D., SUNY Cobleskill, Cobleskill, NY David Waage P.E., SUNY Cobleskill, Cobleskill, NY Contract funded through: - US Department of Defense (DOD) - US Department of Energy (DOE)

2 Pyrolytic process of converting any material (feedstock) that burns into a fuel gas (syngas). Operates in an oxygen starved environment, creating H2, CO, and small amounts of CH4 as flammables. Syngas can be used to operate various combustion based equipment including boilers, gas turbines, and I/C engines. Simple Gasification Concept

3 Waste Feedstock Rotary Kiln Gasifier Ash Raw Syngas Exhaust Gas Air Gas Scrubber Clean Syngas Electricity Hot Water Electrical Generator Cobleskill Rotary Kiln Gasifier Waste to Energy Gasification Plant

4 Many waste materials have excessive moisture. Moisture creates a significant heat load, reducing reaction temperatures. > 1600 F is essential to fully remove volatile matter and thermally crack tars. Common practice is to dry the feedstock prior to gasification. Moisture can be Problem

5 Wet Feedstock Saturated Air and Steam Dryer Dry Feedstock Air Gasifier Ash Hot Syngas 1100 F Cooled Syngas at 300 F Heat Available for Drying at 280 F Heat Recovery Exchanger External Waste Heat Recovery Method for Drying

6 Insufficient heat to fully dry feedstock High efficiency gasifiers (high calorific value gas) do not have sufficient recoverable waste heat for adequate feedstock drying. Notes: High efficiency = 140 BTU/scf, 650 F exit temp Medium efficiency = 100 BTU/scf at 1100 F exit temp. Low efficiency = 60 BTU/scf at 1100 F exit temp. Waste Heat Available for Drying

7 Blending with bone dry feedstocks. Blending with high calorific feedstocks that do not absorb moisture (rubber, plastic, etc). Best solution is to have a gasifier design that can handle the highest level of moisture, produce the highest heating value gas possible and internally recover waste heat to support chemical reactions. Other Means of Moisture Reduction

8 C + H2O -> CO + H2 Reaction is endothermic and requires passing water vapor over hot carbon. 1 lb of water can be converted to 14,300 BTU s (about 44.3 SCF) of flammable gas. About 3550 BTU s of thermal energy is required for each lb of water reacted. Optimum reaction temperature is about 1600 to 1800 deg. F. Moisture can be Converted to Gas.Water Gas Reaction

9 120% Water Gas Equilibrium 100% % of max 80% 60% 40% 20% 0% Reaction Temp Deg F Optimum Reaction Temperature is between 1600 and 1800 F Water Gas Reaction

10 Dry Feedstock HV +q = 376,900 BTU/hr at 44.3 lb/hr Heating Dry Feedstock -q=m*cp*dt -32,560 BTU/hr Vaporize and Superheat Feedstock Moisture -q=m*cp*dt + dhv + dhsh About1546 BTU/lb -4,175 BTU/hr Water-Gas Reaction q=3550 BTU/lb q=-10,000 BTU/hr Convective Heat Losses -q=h*a*dt -18,900 BTU/hr Gasifier At 1600 F Ash Retained Blowing Air 18 scfm -q=m*cp*dt -29,743 BTU/hr Syngas 650F -q=m*cp*dt -16,537 BTU/hr Syngas 32 scfm at 138 BTU/scf -264,960 BTU/hr Balance Net zero BTU/hr 70% Gasifier Efficiency Gasifier Heat and Mass Balance

11 Energy Available for Moisture % of Thermal Energy 70% 60% 50% 40% 30% 20% 10% 0% Heat and Mass Balance for Gasifying Wood Pellets at 1600 F Reaction Temperature 50% 60% 70% 80% Thermal Efficiency of Gasifier % Calorific Value BTU/SCF Minimizing convective losses and internal heat recovery greatly increases thermal energy for moisture No insulation or internal heat recovery With insulation and internal heat recovery Max Calorific Value of Gas Heat Management Frees Thermal Energy for Moisture

12 Max Reaction Temperature Deg F 3,000 2,500 2,000 1,500 1, Heat and Mass Balance Gasifier Operating at 70% Thermal Efficiency No Water Gas Reaction HHV BTU/scf Minimizing convective losses and internal heat recovery greatly increases ability to handle moisture Temp 70% w/o heat recovery Temp 70% w/heat recovery Calorific Value of Gas 0 0 0% 10% 20% 30% 40% 50% Moisture Content in Feedstock % wet basis Temperature can be Maintained with Heat Management

13 Max Reaction Temperature Deg F 3,000 2,500 2,000 1,500 1, Heat and Mass Balance Water Gas Reaction % and HHV BTU/scf Max moisture at 70% efficiency Temp 70% Temp 60% 70% HHV of Gas 60% HHV of gas % Water Gas Reaction 70% % Water gas reaction 60% 0 0 0% 10% 20% 30% 40% 50% Moisture Content in Feedstock % wet basis Maximum Moisture Possible

14 Feedstocks can be mechanically pressed to reduce the moisture within the acceptable range without drying. Design gasifier to operate at the highest thermal efficiency to maximize gas heating value. Possible to gasify wastes with moistures up to 30%, at maximum efficiency, with high reaction temps, and with minimal tar. Summary