Grantee Research Project Results
Final Report: Advanced Slagging Gasifier for Biomass Wastes
EPA Contract Number: EPD06032Title: Advanced Slagging Gasifier for Biomass Wastes
Investigators: Schaffer, Mark
Small Business: Advanced Fibers & Powders, LLC
EPA Contact: Richards, April
Phase: I
Project Period: March 1, 2006 through August 31, 2006
Project Amount: $70,000
RFA: Small Business Innovation Research (SBIR) - Phase I (2006) RFA Text | Recipients Lists
Research Category: SBIR - Waste , Small Business Innovation Research (SBIR) , Pollution Prevention/Sustainable Development
Description:
The objective of this Phase I Small Business Innovation Research (SBIR) project was to demonstrate the ability of an advanced slagging thermal chemical reactor to gasify low ash fusion temperature animal and farm wastes effectively. The primary focus of the Phase I research was on the processing of chicken litter, which has relatively high ash content, high alkali and phosphate content within the ash, and a relatively low ash fusion temperature.
Summary/Accomplishments (Outputs/Outcomes):
The technical activities performed under this project included: (a) waste acquisition and characterization; (b) pilot plant test facility modifications; (c) system gasification testing; (d) process data analysis; and (e) process conceptual design and economic analyses. Three pilot-scale test runs were performed to assess the performance of the slagging gasifier. The first two test runs were performed with auxiliary fuel (natural gas) firing to bring the gasification process up to operating temperature (approximately 2000°F) prior to the introduction of the chicken litter fuel. These test runs were performed at a stoichiometric air/fuel ratio of approximately 90%. The last test run was performed at a stoichiometric air/fuel ratio of approximately 133%, with very little auxiliary fuel addition.
For the first two test runs, the litter feed rate was approximately 22 lb/hr, and the air/fuel ratio was adjusted to allow achievement of the targeted operating temperature. In the third test, the litter feed rate was increased to approximately 49 lb/hr, and auxiliary fuel input was reduced to determine if the process could operate with little or no auxiliary fuel addition.
The operating temperature for the trials was selected on the basis that the process would slag at a temperature of 400°F above the ash fusion temperatures reported in the literature (approximately 1500°F to 1600°F). The slagging behavior for all three test runs, however, was unacceptable.
Advanced Fibers & Powders LLC (AFP) secured typical dried chicken litter feedstock from a commercial supplier of chicken litter manure. System modifications were made to an existing AFP pilot plant facility to accommodate operation under slagging/gasification conditions. The gasification trials indicated that because of the low heating value of the chicken litter (approximately 4,600 Btu/lb) supplemental fuel utilization, air preheating or oxygen enrichment is required to process chicken litter feedstock effectively under slagging conditions. Based on the pilot-scale results, a conceptual design of a commercial scale slagging gasifier integrated with a steam boiler was developed for potential commercial implementation.
The proximate and ultimate analysis of the chicken litter feedstock and the ash is provided in Table 1. The analyses reported in this table were measured by Galbraith Laboratories, Knoxville, Tennessee.
Table 1: Chicken Litter Ultimate and Proximate Analysis
Proximate and |
Galbraith |
|
Received |
Dry |
|
Volatile | 47.05% |
53.96% |
Ash | 28.47% |
32.65% |
Fixed C | 11.67% |
13.39% |
LOD | 12.81% |
- |
Sum, proximate | 100.00% |
100.00% |
C | 30.54% |
35.03% |
H | 5.36% |
4.50% |
N | 3.54% |
4.06% |
S | 0.99% |
1.14% |
Cl | 0.97% |
1.11% |
Ash | 28.47% |
32.65% |
O | 30.13% |
21.51% |
Sum, ultimate | 100.00% |
100.00% |
Ash Minerals as Oxides |
|
Ash | wt/wt |
Na2O | 4.58% |
MgO | 3.62% |
Al2O3 | 3.45% |
SiO2 | 38.40% |
SO3 | 7.11% |
K2O | 8.68% |
CaO | 15.00% |
TiO2 | 0.206% |
Fe2O3 | 1.14% |
P2O5 | 10.90% |
Sum | 93.09% |
Note: LOD is contained in ultimate O and H compositions.
The initial deformation, softening, hemispherical, and fluid temperatures of the chicken litter are provided in Table 2. Measurements for these ash properties were performed by Wyoming Analytical Laboratories, Laramie, Wyoming.
Table 2: Ash Softening and Fluid Temperature Measurements
Reducing Atmosphere |
°F |
Initial Deformation | 2099 |
Softening | 2146 |
Hemispherical | 2205 |
Fluid | 2265 |
The ash softening and fluid temperature of the chicken litter feedstock ash that was tested was at least 300°F–400°F higher than was anticipated. This elevated ash fluid temperature was caused primarily by the higher silica content and lower phosphate content relative to other reported ash compositions. Because of the low heating value of the chicken litter fuel, sufficiently high temperatures could not be achieved in the pilot plant gasifier for suitable slagging performance. As a result, all the trials performed were done in a “dry ash” mode versus a “slagging mode.” To achieve suitable slagging operation, preheated reaction air or oxygen enrichment would be required. Alternatively, the level of auxiliary fuel used would have to be increased. With higher heating value fuels and oxygen enrichment, AFP demonstrated the ability to achieve pilot plant temperatures in the range of 3000°F in trials performed independent of this Phase I project. The composition of the syngas produced during the baseline trial is provided in Table 3.
Table 3: Composition of Syngas at 90% Stoichiometric Air/Fuel Ratio
Gas Species |
Vol % |
Mass % |
N2 (g) | 68.69 |
70.23 |
H2O (g) | 17.50 |
11.51 |
CO2 (g) | 10.05 |
16.14 |
H2 (g) | 1.85 |
0.14 |
CO (g) | 1.80 |
1.84 |
HCl (g) | 0.05 |
0.06 |
H2S (g) | 0.05 |
0.06 |
SO2 (g) | 0.00 |
0.01 |
COS (g) | 0.00 |
0.00 |
Subtotal | 100.00 |
100.00 |
At these operating conditions, most of the syngas energy is available as sensible heat versus chemical latent heat. The lower heating value of the syngas at 1800°F is 154 Btu/lb (11 Btu/scf), and the sensible heat of the syngas is 528 Btu/lb (38 Btu/scf) yielding a total energy content of 682 Btu/lb of syngas. Without the use of air preheat and/or oxygen utilization, the chemical energy content of the syngas is too low to be useful as a syngas. Operating the AFP gasifier with air preheating and/or oxygen enrichment under slagging sub stoichiometric conditions with chicken litter as a fuel, however, can be used for staged combustion to achieve NOx control. Reactor temperatures of approximately 2400°F or greater are recommended for satisfactory slagging operation.
AFP evaluated the use of its chicken litter gasification technology for steam generation and for process heating applications. A technical liaison was established with an industrial boiler manufacturer to address the steam generation application. The purpose of this relationship was to establish feasible interfacing of the AFP chicken litter gasification process with industrial and commercial boilers. Foresight Science & Technology, a support contractor for the U.S. Environmental Protection Agency (EPA), completed a market survey for applications of the AFP gasification system to industrial boilers for process heating applications.
Based on discussions with several chicken farmers and marketing data, AFP focused overall process designs on chicken farms with approximately 1 million chickens or more. Individual farms of this size are common and generate about 15,000 ton/yr of litter. With chicken litter heating values in the range of 4,000 to 5,000 Btu/lb, this results in continuous running heat input of about 150 billion Btu/yr (approximately 17 million Btu/hr). This level of available energy provides some potential for economic process heating and small electric power generation. On-site use eliminates over the road transport and would allow individual farmers to internally resolve their waste disposal problems.
After discussions with several chicken farmers, however, it was apparent that there are no substantial on-site demands for steam and/or electricity by chicken farmers. Therefore, on-site gasification of chicken litter would produce excess quantities of steam or electricity. The amount of steam generated from a 1-million chicken farm is approximately 11,000 lb/hr; the potential fuel cost savings is approximately $880,000 to replace a premium fuel of $8/MM Btu.
On-site generation of electricity using steam Rankine cycles with a 1 million chicken farm indicates a potential to generate about 590 kW of electricity. The potential fuel savings cost is approximately $290,000 per year of revenue generation at a selling price of $0.05/kWe for electricity. At this capacity of power generation, the simple payback (excluding operating and maintenance costs) is greater than 10 years. Heat recovery with electric power generation, therefore, does not appear to be economically viable for on-site use on chicken farms with 1 million birds or less.
Conclusions:
Based on the testing performed by AFP, there appears to be a wide range of ash fusion and fluid temperatures for chicken litter. The operation of a slagging gasifier using 100% chicken litter does not appear to be technically feasible. This is primarily because of the low heating value of chicken litter. To achieve temperatures high enough for slagging operation (i.e., > 2400°F) either air preheating, oxygen utilization, or supplemental fuel firing will be required. Operation of a gasification process at slagging temperatures typically will require stoichiometric ratios close to 1.0. Most of the heat available, therefore, will be in the form of sensible versus chemical heat. Staged combustion for NOx control appears to be the preferred application of sub stoichiometric operation with this fuel. Operation of a gasifier at temperatures below approximately 1500°F would ensure “dry ash operation” with most chicken litters; however, low levels of carbon conversion would be expected with operation under these conditions.
The best economic opportunity for using chicken litter as fuel is to generate steam for poultry processing, animal rendering plants, or other industrial facilities, which require significant amounts of steam. A small facility with a steam demand of approximately 10,000 lb/hr has a potential simple payback of approximately 2–3 years. A larger processing facility with nominally 10 times the steam demand could have simple paybacks in the range of 1–2 years.
The economical generation of electricity will require large plants and favorable sale prices for electricity. AFP believes that the best opportunity for electricity generation will involve the “co-use” of chicken litter in existing coal-fired utility power plants. A separate gasification system to allow slag removal of the chicken litter ash would be preferred to avoid increased fouling and corrosion of the primary boiler. A separate steam generator may even be preferred.
Supplemental Keywords:
small business, SBIR, waste gasification, residual ash, advanced slagging gasifier, poultry litter, concentrated animal feeding operations, CAFO, industrial waste, animal waste, farm waste, carbon conversion, biomass wastes, EPA, renewable energy, green power, broiler litter, biomass, synthesis gas, biogas, waste gasification,, RFA, Scientific Discipline, Sustainable Industry/Business, POLLUTION PREVENTION, Sustainable Environment, Energy, Environmental Chemistry, Technology for Sustainable Environment, Environmental Engineering, energy conservation, waste to fuel conversion, waste gasification, agricultural byproducts, animal waste, poultry waste, alternative fuel, biowaste, agriculture, alternative energy source, animal waste gasifier, bio-based energyThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.