Final Report: Briquettes from Agricultural Residue and Other Wastes for Use in Biomass Syngas Fueled Power Generation

EPA Grant Number: SU834710
Title: Briquettes from Agricultural Residue and Other Wastes for Use in Biomass Syngas Fueled Power Generation
Investigators: Bormann, Noel E , Cadwell, Jillian , Dawn, Mick , Elliott, Ashley , Ferro, Patrick D , Friedman, Alex , London, Mara , Love, Sarah , Parshall, Daniel
Institution: Gonzaga University
EPA Project Officer: Nolt-Helms, Cynthia
Phase: I
Project Period: August 15, 2010 through August 14, 2011
Project Amount: $9,992
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2010) RFA Text |  Recipients Lists
Research Category: Pollution Prevention/Sustainable Development , P3 Challenge Area - Energy , P3 Challenge Area - Materials & Chemicals , P3 Awards , Sustainability

Objective:

This initial phase of the project was to complete the development of and establish performance characteristics for a modular, electric-powered feedstock processing machine that forms corn stover waste into pellets. The machine will accept a slurry waste stream that is added to the corn stover material as both a disposal method and as a way to manage moisture content to improve pellet formation. Development of the machine also incorporated multiple educational objectives while allowing the students to design and fabricate a machine in a multi-disciplinary team. Educational objectives included the need to consider sustainability of the finished machine, consideration of culturally-appropriate methods of support, maintenance and safety, and suitability for construction in Africa. The machine was required to be small enough to be mobile so it can be moved to where agricultural wastes are common in order to increase sustainability and reduce transportation of the biomass. The need to have a mobile capability influenced the project outcomes in several ways.

When completed, the project will greatly increase the sustainability of small gasoline and/or diesel powered generators that are currently used to supplement or replace an unreliable power grid. Use of syngas also will reduce air pollution and carbon emissions when compared to gasoline, diesel, or wood charcoal fuels, and also will reduce the monetary cost of fuel. This feedstock processing equipment will become integrated with the gasifier and generator module in the next project phase to demonstrate a systematic, sustainable method of power generation.

Currently in Kenya, and other places in Africa, the electrical grid is not reliably serving all villages and homes in the rural or interurban areas. Without electrical power, many people suffer a reduction in quality of life and reduced economic opportunity. To address power supply needs, small electrical generators are used, which require diesel or petrol fuels. Use of these fossil fuels is expensive, harms the sustainability of the region, and increases pollution when compared to the option of a syngas bio-fuel. Thus, this project would improve the prosperity of the area, assist the people in sustainable economic development, and reduce pollution compared to the “before project” situation.

To develop the mobile and modular corn stover processing machine the team reviewed current densification methods and subsequently moved through a series of iterative conceptual design and evaluation cycles. This project requires three sub-systems—(a) processing, (b) waste incorporation, (c) densification / pelleting and a material handling method—that together effectively address the objectives presented above. The project team used real “on the ground” information gathered by the project partners, the Catholic Diocese of Kitale (CDK) and the Small World Educational Foundation (SWEF), to develop and evaluate conceptual process designs to select the preferred alternatives. Information gathered from the Kitale, Kenya, area included cost of electrical power, local material costs, availability of types of “salvaged or reusable” materials, workers’ wages, and business attitudes.

The situation for construction of the demonstration machine in Spokane, Washington, is distinct from the cost factors in Kenya, but the team members used locally salvaged and reusable materials to the extent practical both to increase the sustainability of the machine developed and to understand the issues of fabrication with non-standard materials. At the time of this report, the Kenyan Shilling (KSh) exchange rate is 83 KSh = 1.00 USD, the cost of a liter of diesel is 100 KSh ($4.55/gal), and an agricultural worker earns between 200 to 300 KSh per day.

A hammer mill was fabricated using salvaged 18-inch diameter steel pipe for the case and 12 discarded connecting rods from a car engine for hammers. Power is provided by a reused 5-hp (3.8 kW), 220-volt, single-phase motor driving v belts. This hammer mill will process the corn stover into particles suitable for densification.

Based upon a review of the literature about densification of agricultural biomass (Morey, 2005), a roll press was the approach initially investigated for densification. Evaluation of fabrication costs for the roll press reduced its preference and other alternatives were evaluated: batch-hydraulic press, hydraulic press cycling, trip-hammer, and finally the preferred small roller and die pellet mill. The cost of materials needed in fabricating a roller and die pellet mill in Spokane was estimated to be between $1,100-$1,300 plus $600-$900 in machine shop costs. A commercially produced pellet mill was sourced at $2,700. The economies of scale present in the commercial machine makes it a more attractive option because the limited use of salvaged material and the complex welding and fabrication of the pellet mill on an individual basis would make Kenyan manufacturing of a pellet mill less routine and, therefore, unattractive.

The mixing of a slurry waste is accomplished by using a salvaged, single-cylinder, two-cycle engine from a weed trimmer to act as a positive displacement pump. Waste is connected from a barrel or bucket to the pump with flexible tubing and then to the mixing point in the auger. The material is moved by a salvaged auger from the hammer mill to the pellet mill. Pellets are collected in metal baskets to cool and for loading into the type of locally-sourced fiber sacks used to transport shelled corn kernels throughout Kenya. The team has prepared a construction design package and an operation and maintenance manual for the machine.

The machine is sized to process between 100 and 200 lb./hr. (50-100 kg/hr.) of corn stover. The machine is assumed to be operated six days a week, six hours a day for a period of four months each year following the corn harvest, providing between 57,000 and 115,000 lbs. (25,900-51,800 kg) of pellets annually. Based on production rates obtained from Kenyan farmers, this annual production would process the stover from no more than approximately 360 acres (145 ha) of corn plantings. Estimates are that the biomass pellets can produce 0.50 kW- hr/lb., and to produce the pellets consumes approximately 0.1 kW-hr/lb. The net energy content for the pellets would then be estimated at 0.40 kW-hr /lb. The net electrical energy from the biomass from 360 acres of corn would be between 22,800 kW-hr and 46,000 kW-hr and have a monetary value of between $4,560 and $9,200 at $0.20/kW-hr. Use of a biomass syngas for the production of this amount of net power would replace the consumption of between 2,760 gallons and 5,520 gallons of diesel fuel for a 10 kW generator, and that displaced fuel would have a current monetary cost of between $12,558 and $25,116. These estimates of machine performance that lead to the net energy of the pellets will need to be confirmed when complete testing of the system is finished. Until confirmation is possible, the project team has used a Monte Carlo simulation of performance models to provide a distribution of likely performance measures.

Safety is a primary goal of the project. The safety of the operator is addressed from the standpoints of exposure to dust, noise, flying fragments, waste, and moving machinery parts. All five of these concerns were considered during the development.

The purchase, collection, transportation, and processing of the stover and pellets are costs of the biomass fuel and are estimated based on the information from project partners.

Summary/Accomplishments (Outputs/Outcomes):

The demonstration machine developed in this project appears to provide a feasible and effective method to meet the project objectives. However, thorough performance testing of the machine has not been completed. Completion of Phase II of the project will confirm performance estimates for power production. At this time, estimates of the financial performance are based on the information received from the project partners in Kenya.

The most uncertain cost estimated will be the price that must be paid to each farmer to provide the stover material to the machine operator. Monte Carlo simulation provides a distribution of the estimated costs of the stover. Estimates are based on a rate for collection of 150-250 lbs. (75- 125 kg) of stover per hour of labor for eight hours each day. A preliminary estimate for the cost of the stover material ranges between $0.015 and $0.04 USD/lb. (1-3 KSh/kg). Simulation provides a range of total material cost at the location of the machine of between $300 and $5,200 USD. The operation of the machine will require two people to process and load the resulting pellets into the sacks for storage. The cost of labor to operate the gasifier system is estimated to range between $1,090 and $2,515 USD.

Machine maintenance is estimated to be 15% of the machine cost each year for a 5-year life.

The total estimated annual costs, including material, operation and maintenance, plus purchase amortization range from $6,060 to $10,590 USD (503,000 – 879,000 KSh). In the Net Annual Benefit table, Table 1 below, this cost is compared to (a) the avoided cost of diesel fuel and (b) the assumed value of electrical power produced.

Table 1: Net Annual Benefit

Economic Measure

Lower Bound of 90%
Range

Upper Bound of 90%
Range

Total Annual Costs to Produce Biomass
Pellets

$1,490 USD
123,700 KSh

$3,770 USD
313,00 KSh

Value of Electrical Power (net) contained
in biomass pellets @ $0.20/kW-hr.

$2,600 USD
215,800 KSh

$5,200 USD
431,600 KSh

Avoided cost of diesel to produce
equivalent amount of electrical power

$7,330 USD
608,400 KSh

$14,600 USD
1,216,800 KSh

Note that the above results do not monetize environmental benefits of the use of the bio-fuel pellets. The net power incorporates the amount of energy consumed by the processing machine to produce the pellets. The total cost to purchase and fabricate this demonstration processing machine is estimated as $3,800 USD with $3,087 spent at the time of this report. The estimated machinery costs for Phase II of the project are $4,500 USD for a 10kW generator and engine and $4,900 USD for the gasifier needed to fuel the generator. Diesel and biogas motor generator sets, or gensets, cost the same. The analysis of purchase financing and monetary results, using Monte Carlo simulation with the probability of various monetary predictions identified, is addressed in detail within the project report. These detailed simulations indicate an 84.3% probability that this biomass syngas fueled generator project can achieve a 15% annual return on investment, excluding the monetized benefits that are not easily established for using non-fossil fuels to generate power in the Kitale, Kenya, area.

Conclusions:

Based upon estimates of costs of production of biomass pellets from this Phase I project and preliminary estimates for using the biomass pellets to make a syngas fuel for electrical power production in a Phase II project, the project appears feasible to implement.

Interactions between the costs of diesel and the purchase cost of the corn stover biomass have the largest influence on the predicted monetary performance of the project.

Supplemental Keywords:

energy conversion, biomass costs, monte carlo simulation

Relevant Websites:

Center for Engineering Design & Entrepreneurship Exit

Progress and Final Reports:

Original Abstract