Harley Sietsema, president, Sietsema Farms, said that around five years ago the U.S. Environmental Protection Agency and the Michigan Department of Environmental Quality (MDEQ) were talking a lot about nutrient management plans for anyone using manure from a confined animal feeding operation (CAFO).
“I was worried that I wouldn’t be able to sell poultry litter to crop farmers because the next step was going to be that EPA would require the crop farmers to have a nutrient management plan if they used any livestock waste and as onerous as that can be, the crop farmer might just say to heck with it and buy commercial fertilizer,” Sietsema said. “I didn’t want to get in the position down the road where I had a problem with litter. I wanted to solve it and get some indirect value out of it if I could.”
An innovative coupling of a starved-air low-temperature (SALT) gasification with a hot-air turbine is hopefully going to provide the solution that Sietsema is looking for when it goes online in later this summer.
Sietsema Farms raises 1.3 million head of heavy toms per year for Michigan Turkey Producers LLC and also operates a 10,000 sow, farrow-to-finish multiplier operation for Newsham Choice Genetics. Sietsema’s feed mill produces around 2,500 tons per week of pelleted feed for the turkeys and the sows. Current utility costs for the mill run around $500,000 per year for natural gas and electricity. “We intend to replace the majority of our natural gas and electricity needs from the utility companies with the energy this project produces,” Sietsema said.
Heat Transfer International (HTI) has designed and built the 23 million BTU per hour gasification system for the Sietsema feed mill. Coupling the gasifier with a hot air turbine and a boiler allows the system to produce 0.5 megawatts of electricity and 8,800 pounds per hour of steam at 150 pounds per square inch. Operating at capacity, the system will consume 70,000 pounds of turkey litter per day.
HTI’s roots were in developing gasification systems used for extracting precious metals from industrial sludges (www.heatxfer.com). Low-temperature gasification converted the sludge into a combustible gas, known as synthesis gas or syngas, while leaving the precious metals concentrated in the ash. Employing SALT gasification with litter produces a very clean burning syngas and an ash product that concentrates the phosphorous, potassium and many of the other trace minerals found in the litter. The ash content should be around 15% of the weight of the litter.
The gasifier is a retort, fixed bed gasifier which is around 12 feet by 20 feet. To start the gasification process, litter is introduced into the gasifier and is heated at low temperatures. As the litter is “roasted” at low temperatures in the gasifier, the resulting syngas produced is sent to a separate chamber, the oxidizer, for combustion of the syngas to produce heat/energy. Restricting the oxygen level in the gasifier to 10-15% limits the amount of combustion in the gasifier and maintains the temperature in the chamber at 600-700 F. According to Dickinson, keeping the temperature low inside the gasifier retains any of the “nasty” compounds in the ash as a solid. Most of the carbon and nitrogen in the litter is gasified.
The heat/energy produced in the oxidizer then travels to an air-to-air heat exchanger where heat is transferred to filtered room air and sent to the hot-air biomass-turbine. After exiting the turbine, this clean heated air can be used as preheated air added back into the gasification process or used for other food grade processes.
After the high-grade heat travels through the air-to-air heat exchanger, the low-grade heat travels to the waste heat boiler to produce steam. Patrick Dickinson, business development manager, HTI, said that the thermal efficiency of the system is expected to be 70-75%.
Dickinson said that the SALT gasification system burns so cleanly and efficiently that it doesn’t require any specific air pollution control devices for the emissions to be well below any regulated limits set by MDEQ. The complete gasification, electrical and steam generation systems at the Sietsema feed mill will have a footprint of around 3,500 square feet of floor space. In addition to producing power and steam, systems can be designed to provide hot air, chilled water and hot water.
Litter handling and value
Sietsema Farms has litter storage areas on all of its farms. Litter will be stored at the feed mill inside the gasifier building in a separate feedstock room. Negative pressure ventilation will be used to control odor outside the building, as air for the roasting and combustion will be drawn through this room. There will be storage for around a weeks worth of litter at the feed mill.
The average distance from the turkey farms to the Sietsema feed mill is 40 miles. Organic farmers have created a market for poultry litter, and Sietsema said that his company may continue to sell some of its litter or clean out houses on other farms to get more litter to satisfy the energy needs of the feed mill and provide fertilizer for existing customers.
Dickinson said that the general rule of thumb for biomass energy projects is that the biomass material should be in close proximity of the gasification process and should have a low cost, or better yet, have someone willing to pay a tipping fee for accepting their waste. He said that projects tend to get tougher to justify financially the more you have to pay for biomass.
Other sources of revenue
The roughly 10,000 pounds per day of ash that the gasifier will produce has some economic value, but Sietsema is not sure yet what that will be. Companies that use anaerobic digesters are looking at combining the ash with the solids from the digester and pelleting this to make commercial fertilizer. Sietsema said that fertilizer manufacturers and cement companies have also expressed interest in the ash.
Exhaust gases leaving the system are expected to be around 350-400 F. Some of this heat could be captured and put to work doing something like drying grain.
There may be opportunities in the future to utilize other forms of biomass in the gasifier that either have no cost or can provide a revenue stream. Some municipalities pay composters to receive things like leaves and ground tree branches, these and other forms of clean biomass that are currently being disposed of in landfills could be gasified instead. Sietsema said that MDEQ requires emission tests be performed on any different fuels run through the gasifier.
Sietsema said that his company is still in negotiations with utility companies over the charges for standby power and the price received for electric power sold back to the utility. Because the electricity is generated with biomass and is renewable, Sietsema Farms may sell power to the grid at a “green” power price and buy back power from the grid at a lower price.
Sietsema said that his company has invested several million dollars in this project. Some of this investment has been offset by grant money received, $250,000 from the State of Michigan’s Julian Stille Fund and $500,000 from the USDA. Dickinson estimates that a project of this size would have a turn key cost of around $4 million.