Non Technical Summary
We propose a solution to greatly reduce the cost of biomass-to-power. This would improve the sustainability of forest resources by reducing the carbon footprint of decaying biomass and the cost of wildfire prevention through forest fuel load reduction. It would also develop value-added products from woody resources (electricity, biochar fertilizer) increasing the productivity of forest lands.Biomass gasification is a well-known process to convert biomass from solid to a gas that an engine generator can burn to generate electricity. It could fundamentally use low cost equipment and scale down to be physically close to biomass feedstock sources. Currently, however, more than half the cost of biomass gasification to power is in produced gas pretreatment to remove organic contaminants (tars) that cause equipment fouling within hours. We propose using the internal combustion engine itself as the produced gas clean-up hardware as well as the power generation, achieving significant cost savings of more than 50% while also enabling a small, portable system that can be moved close to biomass sources, considerably reducing feedstock transportation costs.The concept was invented and proven at MIT. To bring the technology closer to commercialization, Plasma Energy Innovation, an MIT spin-off will, as part of this project, test the technology using minimally processed forest biomass (woodchips). Based on the experimental results, we will also develop a technoeconomic model of full system operation to prove its financial viability.If the project is successful, it could really introduce a paradigm shift in the cost of small scale biomass to power systems. A proven, low cost biomass to power system could have significant implications for reducing GHG emissions and improving energy security in the US by utilizing biomass that is otherwise wasted. It can also help provide financial growth for rural communities and forest management organizations by providing additional revenue streams (electricity, biochar).

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
402	5310	2020	100%

Knowledge Area
402 - Engineering Systems and Equipment;

Subject Of Investigation
5310 - Machinery and equipment;

Field Of Science
2020 - Engineering;

Goals / Objectives
There is a clear and unmet need for transformative technologies to improve biomass to power systems by reducing their cost and complexity to make them competitive with fossil fuels. The big hurdles in biomass to power have always been the cost of transporting biomass over long distances and when using gasification, the cost of cleaning up the heavy organic components (tars) in the gasifier producer gas. These tars deposit on surfaces and force frequent maintenance of the equipment.The goal of this project is developing a novel technology to drastically reduce the cost of power generation from biomass waste (forest and agricultural). The end result will be a portable, biomass to power system based on internal combustion engines. The technology can be used to generate clean, sustainable power, locally, from biomass waste that would otherwise generate more greenhouse gas emissions if allowed to decay on its own (sustainable bioenergy and reducing climate change are program priorities). Forest trimmings can be easily converted to fuel (wood chips) which the proposed biomass to power unit can use thus significantly reducing the cost of wildfire prevention through forest fuel load reduction (a program priority). The electricity produced from biomass waste can be used locally or sold to the grid, providing a source of income for farmers and forest management professionals. Furthermore, the ash and char residue obtained from the gasifier has excellent soil quality enhancement properties and can used as a fertilizer. This technology would provide financial growth in rural areas using local resources which would otherwise have to be disposed as a waste. If successful, the technology will help farmers and forest management authorities monetize local woody biomass waste materials. The present application has a direct connection to agricultural and forest-related manufacturing technology, energy efficiency and alternative and renewable energyCurrently, more than half the cost of biomass and waste-to-power systems is in synthesis gas pretreatment to remove organic contaminants (tars). This is especially true for small scale systems that are required to be closer to the biomass source and minimize transportation costs. In the present application, we propose to use internal combustion engines as the synthesis gas clean-up hardware as well as for complete combustion for power generation, achieving significant cost savings of more than an order of magnitude. The concept of gas cleaning is based on extremely fuel rich hot intake gas partial oxidation in an engine. If the producer gases are kept above the tar dew point (~250 C) before they are inducted into the engine, tar condensation and thus fouling is prevented. The tars are then destroyed in a very fuel rich combustion where a small amount of air is provided to destroy the tars while leaving enough heating value in the exhaust. The cleaned producer gas in the exhaust is subsequently burned to completion in another engine to produce power.The objectives of Phase I of this project will involve experimentally proving tar removal from producer gas generated through gasification of different types of minimally processed waste woody biomass (woodchips from forestry enterprises) in the gasifier for their performance. We have already proven the concept at our laboratory at MIT using commercial wood pellets. Integration between gasifier, clean up engine and power generation engine will be examined to improve efficiency while considering combustion control challenges. We will model the overall system in terms of a techno-economic evaluation of potential savings not only from the cost of tar cleanup but also from reducing transportation costs by using a smaller system. Phase 1 of the proposal aims to further prove the technology concept and develop it to the point where it is ready to be used in small scale biomass to power applications, where a large and growing market exists. Addressing the current and significant unmet market needs by providing an inexpensive, robust, turn-key biomass to power solution with clear technical and cost advantages over the state of the art, will enable rapid adoption of the technology.In summary, the objectives of the project will be:To demonstrate operation of the system using woodchips instead of wood pellets.To develop a technical model of the physical system in order to size components for the applicationTo develop a technoeconomic model of the system operation and evaluate its financial viability e.g. in terms of levelized cost of electricity.

Project Methods
Work PlanThe focus of this project work plan is to verify the performance of an integrated gasifier to power system that demonstrates the hot rich combustion cleanup process and its potential to significantly reduce the cost of biomass to power using real forest and agricultural waste biomass.Task 1.0: ModelingWe will carry a parallel modeling effort throughout the program to gain insight on the performance of the system. We will use both chemical kinetic models (CHEMKIN, using appropriate mechanisms), internal combustion engine-based codes (GTPower, AVL Boost) and process simulations (ASPEN). Once we have developed models, optimization of the system can be performed. Optimum total system size will also be explored by factoring in transportation cost using the USDA Forest Residue Transportation Model. The optimization process using this approach is much simpler than empirical optimization.Subtask 1.1 Engine ModelingAn engine gas dynamics/thermodynamics model (based upon AVL Boost software) will be used to improve the understanding of using engines as tar cleanup chemical reactors. We will use the model to provide specifications to the engines, such as inlet conditions, compression ratio, optimum valve timing. The in-cylinder pressure and temperature profile will be generated and used to better understand which mechanisms (cracking, oxidation) lead to tar destruction. we will use both measured gasifier gas composition, as well as data from the literature.Subtask 1.2 Chemical kinetic calculationsWe will use state of the art chemical kinetic mechanisms in the CHEMKIN software to provide guidance on using an internal combustion engine as a partial oxidation /tar cracking reactor. The in-cylinder pressure and temperature profiles from AVL Boost will be used as inputs. Optimal conditions for maximum tar destruction will be specified. We will also optimize biomass to power conversion efficiency and flammability/ combustion stability in the second (complete combustion engine).Most importantly we will model auto-ignition in the second, power generation engine, based on the stoichiometry (λ) used in the first (cleanup engine). Increasing λ in the first engine (less rich combustion) destroys more of the tar but leaves less heating value for the second engine. That can be compensated by eliminating the heat exchanger between the two engines and burning hotter in the second engine. That will improve combustion stability but increase the chances of engine knock. We will use CHEMKIN software to predict knock in the end gas of the second engine (spark ignited). We will also model the mixture's laminar flame speed as a proxy for turbulent flame speed and thus combustion stability. Initially we will assume spark ignited, stoichiometric operation for the second engine, but lean, HCCI operation will also be explored if the resulting maximum rates of pressure rise are acceptable for safe operation.Similarly, to the previous subtask, we will use both measured gasifier gas composition, as well as data from the literature.Subtask 1.3 Process SimulationThe complete process from biomass to power will be simulated using a series of reactor to model the gasifier (assuming equilibrium which is a good assumption for downdraft gasifiers) in software such as Aspen Plus. Empirical parameters tuned to match experimental data will be used. Engine and chemical kinetic modeling (GT Power) results will be used to change gasifier flowrate as a function of engine rpm and λ. We will explore opportunities for optimally sizing equipment such as gasifier size versus engine displacement volume and rpm. We will also explore optimizing the second vs. first engine in order to minimize total CAPEX per kWe.Task 2.0: Tar Cleanup Engine Experimental Performance In this task, we will use our experimental setup that includes a downdraft gasifier connected to an engine to test real forest biomass waste material (woodchips. The setup was so far run on sawdust pellets.Subtask 2.1 Testing the gasifier with woodchips. We will adjust operating parameters such as fuel air ratio in the gasifier to ensure smooth operation without bridging, high temperature in the producer gas and low particulates. The producer gas composition will be characterized using our NDIR analyzer. Different types of woodchip feedstock will be tested with different moisture and ash content. Due to the lower heating value of the woodchips, we will need to increase the gasifier feed rate compared to pellets. For the pellet experiment, we have simply been manually feeding the gasifier. For woodchips, we may need to re-install and modify an original hopper system that came with the gasifier. Furthermore, for the pellet experiment, we used the suction of the room ventilation system for startup and once the gasifier was in steady state, we switched to the unthrottled engine suction to operate the gasifier in induced draft mode. For woodchip operation, the hydraulic resistance of the feed will be much lower and thus the available suction, may have to be adjusted through a valve to operate the gasifier in optimum fuel/air ratio. This tuning will have to be done experimentally. Subtask 2.2 Connecting the engine and testing tar destruction. Different fuel air ratios will be tested as well as engine shaft speeds (hence altering residence times). Tar concentration will be measured before and after the engine. Tar composition will be analyzed using High Performance Liquid Chromatography(HPLC) or combined GC-MS and Thermogravimetric analysis.Task 3.0: Performance Check and EconomicsThe overall performance of the gasifier/engine system will be evaluated for power generation in terms of efficiency and economics. The heat integration will be considered between the engine and gasifier to improve the overall efficiency. The cost analysis of the system will be performed if it has to be implemented on a large scale.We will use ASPEN plus to perform the system evaluation. There is no reciprocating reactor in ASPEN, but we have modelled one previously using rotating machinery followed by adiabatic reactors and expanders. The purpose of this effort is to determine the energy and mass flow balances, as well as a preliminary attempt to use a thermally integrated system. We will use models for the engine to determine tradeoffs between engine compression and external compressors. Additionally, we will factor in the cost of biomass transportation as a function of distance from the biomass source by using for example the USDA's Forest Residue Transportation Model [USDA]. This will help us optimize system size for minimizing both transportation and equipment costs.Task 4.0 Report WritingThe results and recommendations will be summarized in a detailed report. The final criterion to evaluate the success of the project is the expected levelized cost of electricity of the complete system designed based on the experimental data.This completes the phase I of the project. Upon completion, this will set up a platform for Phase II where we would demonstrate a full scale system including the power generation engine and power generation controls.