Combustion of Poultry Litter: A Comparison of Using Litter for On-Farm

Space Heating Versus Generation of Electricity

John P. Chastain, Ph.D.Professor and Extension Agricultural Engineer

School of Agricultural, Forest, and Environmental Sciences

Waste to Worth Conference, Denver, Colorado

Grand Hyatt Hotel • April 1-5, 2013

Using Manure For Energy Is an Old Idea

People have used manure as an energy source for thousands of years.

Dried dung was used as fuel for ovens and open fires.

More recently: making biogas from slurries, Combustion in a furnace, or using pyrolysis and exhaust-gas reburn.

Poultry Litter Contains a Significant Amount of Energy

Average HHV = 6202 Btu/dry lb If litter has a moisture content of 24%

the LHV is 4480 Btu/wet lb. Unfortunately we cannot use all of this

heat. No method of heating or generating

electricity is 100% efficient.

How much litter is in one 42’ x 500’ broiler house?

Estimate based on measurements in a SC broiler house.

So for a 6-house farm the litter production

= 846.8 tons/year.

Litter Depth = 5.675 inMoisture Content = 24 %

Bulk density = 28.4 lb/ft3

Floor Area of 1 house = 21000 ft2

Litter volume = 9931.25 ft3

Mass of litter / house = 141.13 tons/yr

Can we burn this litter on-farm to off-set LP gas needs?Will we have enough?

Several groups and companies are developing poultry litter furnaces

Turkey litter in Missouri (on-farm heat)

Broiler litter in Arkansas (Tom Costello, on-farm heat).

American Heat and Power (Habetiz and Echols, power plant)

Brisco Farm, Mo. www.

ecoagri.biz

http://www.americanheatandpower.com/PoultryLitterEnergy.html

The efficiency of the poultry house determines how much LPG is needed.

Table 2. Estimates of annual LP gas use for heating in broiler houses based on house energy efficiency and number of flocks grown per year.

 Level of Broiler House Energy Efficiency

5 Flocks per Year

5.5 Flocks per Year

gal LP per year per 1,000 square ft of house

Very efficient 120 132Efficient 150 165Average 180 198Low 200 220Very low 270 297

LP Gas use measured on SC broiler farms: “Typical” Values

LPG Use Rate = 240 gal LP /1000 ft2/yrLPG Use / house = 5040 gal LP /yr

LP Use / 6-house farm = 30240 gal LP /yr

Need an estimate of overall heating system efficiency.

Heating system efficiency takes into account the efficiency of the furnace and the efficiency of distributing the heat to the broiler house.

It can be as low as 20% with 40% being a reasonable target (Costello, 2007).

So that means for every 1000 Btu of heat in the litter only 400 Btu will be used to heat the house!

So how much heat is in the litter on a 6-house farm?

With this heating system 1 ton of litter can replace 38.75 gal of LP!

litter/6-house farm = 846.8 tons/yrHeat Value of Wet Litter = 8960000 Btu/ton

Heat Content = 7587309744 Btu/yearHeating System Efficiency = 40 %

Heat delivered to houses = 3034923898 Btu/yearEnergy Content of LP = 92,500 Btu/gal LP

LPG equivalence = 32810 LPG Eq./yearLPG Eq./ton of litter = 38.75

So would there be enough litter to heat these houses?

Produce 846.8 tons/year Need 30,240 gal LP/year 1 ton of Litter replaces 38.75 gal LP So I need: 30,240 gal LP

÷ 38.75 gal LPG Eq./ton = 780.4 tons

(66.4 tons extra?) Yes, if heat can be produced and delivered when

needed. Expect 80% to 100% depending on weather.

Need to remember that burning litter will produce ash that must be managed.

Litter ash cannot be used as a lime substitute.

Has high concentrations of P, K, and minor nutrients.

Does not contain N. Must be spread based on P2O5 or K2O.

How much ash and plant nutrients will be produced?

1 Broiler 6-HouseHouse Broiler Farm

Ash production if 100% of LPG is off-set (ton/yr) 24.4 147Plant nutrient yield in ash

P2O5 (ton/yr) 2.20 13.2

K2O (ton/yr) 1.90 11.4

Ca (ton/yr) 1.40 8.4Mg (ton/yr) 0.30 1.8S (ton/yr) 0.28 1.7Zn (lb/yr) 35.6 214Cu (lb/yr) 37.6 226Mn (lb/yr) 43.5 261

How much land is needed?

1 Broiler 6-HouseHouse Broiler Farm

Ash production if 100% of LPG is off-set (ton/yr) 24.4 147

Plant nutrient yield in ash

P2O5 (ton/yr) 2.20 13.2

K2O (ton/yr) 1.90 11.4

Land area needed if ash is spread based on 89 lb P2O5/ac (acre/yr) 49.4 296

Ash application rate (ton/acre) 0.49

Land area needed if ash is spread based on 45 lb K2O (acre/yr) 84.4 506

Ash application rate (ton/acre) 0.29

What is the value of the ash if spread based on P2O5 for a 6-house farm?

Value of P2O5 = 13.2 ton/year x 2000 lb/ton x $0.69/lb = $18,216/year

Value of K2O = 11.4 ton/year x 2000 lb/ton x $0.50/lb = $11,400/year

Total value = $29,616/year Can this be used for the poultry producer’s

cropping enterprise?

What would the savings be if litter replaced LP? – Scenario 1: Use ash on own land. LP gas for a 6-house farm = 30,240 gal/year Assume price is $1.90/gal Value of LP savings = $57,456 However all N was lost in the litter that was burned

– 780.4 tons burned. PAN = 44 lb PAN/ton @ $0.71/lb N-lost was worth $24,380 P & K Value = $29,616/year Net gain = $62,692/year (LP saved – N lost + P&K)

What would the savings be if litter replaced LP? – Scenario 2: No land - brokerage LP gas for a 6-house farm = 30,240 gal/year Assume price is $1.90/gal Value of LP savings = $57,456 Brokerage payments lost on the 780.4 tons burned. Litter price = $15/ton Loss of Brokerage Payment = $11,706 P & K Value = ($29,616/year x 0.33) = $9,773 Net gain = $55,523/year (LP saved – Loss + P&K/3)

The big questions is… Can annual savings of $55,523 to $62,692

per year pay for the heating system fast enough?

Cost to produce an LPG Eq. is about $0.55 to $0.65/LPG Eq. in other systems studied.

Assume we can make a LPG Eq. for $0.65. 30,240 gal LPG Eq. x $0.65 = $19,656/year Annual savings is closer to $35,867 to

$43,036 per year.

Value per ton of litter Burned 780.4 tons of litter Annual savings $35,867 to $43,036 per

year. Value of litter =$46 to $55/ton

Electricity use based on data collected on SC broiler farms

Cost per kWh = $0.077 to $0.122

kWh Use Rate = 2326 kWh/1000 ft2/yrkWh Use / house = 48846 kWh/yr

kWh Use / 6-house farm = 293076 kWh/yr

Can litter be burned to generate electricity?

Yes – but may not be cost-effective on-farm

Need a steam boiler and turbine. Cost to produce a kWh is high for small units.

Smallest units are on the order of 1000 kW.

Average overall efficiency for coal-fired, steam power plants in the US is 32%. (Beer, 2012)

Most of the energy in the fuel is lost as heat.

To run a 1 MW plant requires (Chastain et al., 2012)…

Biomass fuel feed rate = 2381 lb litter /hr Need 10,429 tons of litter / year! Gross energy production

= 8,759,891 kWh/year Gross kWh/ton of litter = 840 Need 74, 42’ x 500’ broiler houses

Net kWh for a 1 MW plant (Chastain et al., 2012)…

Gross energy production

= 8,759,891 kWh/year Gross kWh/ton of litter = 840 Need 74, 42’ x 500’ broiler houses Electrical use by houses

= 3,614,604 kWh/year Net energy to grid = 5,145,287 kWh/year Net kWh/ton of litter = 493 (59%)

So only 590 kW of a 1000 kW power plant would be available to supply energy to something besides the farms that generate the litter.

Not horrible, but needs to be considered!

Nothing is 100% efficient!

Makes co-firing of coal & litter look attractive.

A 1 MW litter powered plant will produce…

1957 tons of litter ash. 176 tons of P2O5.

152 tons of K2O Using our previous price assumptions the ash

has a value of at least $394,880. Seems like a larger power plant would be

needed to justify construction of a fertilizer plant.

Results for a Single Farm with Best Assumptions 1 broiler house can support 13.5 kW. A 6-house farm could operate a 80 kW generator. The on-farm generator could produce 711,312

kWh/year 293,076 kWh per year could be used on-farm. Excess would be 418,236 kWh/year Potential value = $0.12 x 293,076 + $0.045

x 418,236 = $53,990/year

Are you lowering your costs in this case? Value of electricity = $53,990/year The lowest price to produce a kWh in this system is

about $0.08/kWh. Lowest cost to produce = 711,312 kWh/year

x $0.08/kWh = $56,905 /year Are you making money for your trouble? No. Loss of at least $3000 / year or $3.54/ton of

litter (-$3000/846.8 tons/year).

Conclusion Using litter for heating is the only on-farm

alternative that makes sense at this time. Value of litter (100% use) will range from $46 to

$55/ton Matching heat demand is tough and will prevent

100% utilization of litter for combustion. Need large scale to be in the electric power business. Key is to understand cost to produce energy on farm

which will vary greatly.

Agricultural Mechanization &

Business

School of Agricultural, Forest, and

Environmental Sciences

Contact:

Christi Leard

864.656.3250

ccampb3@clemson.edu

http://www.clemson.edu/cafls/safes/agmec/