<< oH4 P

PM W

O tJMpq »,

>H

<! £

>->p

!>i WH >M Wi-l

1 M Wm X

<l Pi c/:W O <

A FEASIBILITY STUDY OF A BIOGAS PIANTFor The

Evergreen DairyLittlerock, Washington

«J

May 23, 1980

ByStudents of the Energy Systems Program

THE EVERGREEN STATE COLLEGEOLYMPIA, WASHINGTON

1979-1980

FEASIBILITY STUDY OF A B10GAS PLANT

AT THE EVERGREEN DAIRY

LITTLEROCK, WASH.

MAY 23, 1980

Researched by; Energy Systems Program (1979-1980)The Evergreen State CollegeOlympia, Wash, 98505

Students: David GerstenbergerMike LounsburyKerry MalloyMark Young

Faculty; Dr, Jacob 8, Romero

* The Evergreen State College reserves proprietary rights to allinventions resulting from this study.

TABLE OF CONTENTS

Page

Abstract i

I, Introduction 1

Background 1

Conclusion and Recommendations I

II, Farm and Site, Descriptions 2

111= Proposed Biogas Plant 5

Baseline Design and Operation, 5

Alternative Designs 7», .

IV, Feasibility Results 8

Economics 8

Process Analysis 8

References 13

ABSTRACT

A biogas producing plant at the Evergreen Dairy, Littlerock, Washington,is technically feasible and economically attractive. The plant willproduce 26,200 ft /day of biogas, which is in excess of the dairy processneeds by 3,370 ft: /''day. The energy produced can completely supplantthe 2,000 gal. of oil presently used, and has an annual value of about$29,700. In addition, fertilizer valued at $15,300 is produced for atotal earning of $44,900,

The cost of the biogas plant is approximately $140,000. If the dairyused the total earning to pay for the loan, the payback period is about9 years,

—i—

I. Introduction

Background

The purpose of this report is to study the feasibility of an on-sitemethane digester for the Evergreen Dairy located in Littlerock, Washington.Murray Wicks and Doug Peters of the Evergreen Dairy approached us, theEnergy Systems program at The Evergreen State College, in early springof 1980, xdth a request to look into the feasibility of a methane plantwith the aim of the dairy becoming energy self-sufficient. The EnergySystems program agreed to conduct a preliminary study as part of an academicresearch project aimed at understanding and implementing energy alterna-tives.

The Evergreen Dairy is a privately owned, modest-sized enterprise whichprocesses its own milk, For the process it uses substantial amounts ofhot water and steam and presently burns about 2SQOO gallons of oil permonth in their boiler.

The scope of this study was limited to defining the process and assessingits technological and economic feasibility. Because of the short timeavailable, a detailed design of the components was not attempted. Includedin the study are a plant layout, a process design, heat and materialbalances, production arid economic results. The results obtained aresufficiently attractive that a further detailed design study leading toimplementation of a biogas plant is warranted.

Conclusions and Recommendations

The results of the analysis show that a methane plant at the EvergreenDairy could produce 26,180 ft of biogas per day. This ±s 3,370 ft3per day in excess of what is needed to make the dairy energy self-sufficient o Thus from the viewpoint of energy production the biogasplant is very attractive.

The projected cost of the plant: is about $140,000, The gas produced bythe biogas plant will earn the dairy about $29,700 per year in fuel costsand produce close to $15,300 in fertilizer value. A 10 year loan at 15% wouldrequire an annual interest payment of $40,600. With the combined valueof the fuel and fertilizer the payback period is about 9 years,.

The costs of fuel and fertilizer will continue to climb and it may becomeimpossible to keep up x^ith the increases. It is the recommendation ofthis study that the Evergreen Dairy continue, in their plans to financeand build a biogas fuel plant.

-1-

The Evergreen Dairy is located in Littlerock, Washington, about tenmiles south of Olympia (see. Figure A), The dairy has approximately700 jersey cows of which 360 are being milked, The cows are housedyear-round in concrete floored stalls. Manure from the loafing shed(360 cows) is hosed out daily while manure from an, upper shed (300 cowsplus bedding material) is scraped out, Manure is washed into a holdingtank and pumped out to the fields daily. All the milk is processed onsite at the farm's creamery (see Figure B - building layout). Five peopleare employed to operate the farm and creamery. At present 250,000 gallonsof milk and 70,000 Ibs of butter are. produced yearly. Cheese and icecream production is expected to begin in fall 1980, The dairy is surround-ed, by 320 acres of field where they grow corn and hay for feed,

The proposed digester site is located at the edge of the field west ofthe main cow shed. The digester site was chosen to minimize pipingdistance from both the existing conditioning/holding tank and the boilerroom (Figure B).

-2-

FIELD -'

FROFCSEDD'uirESTER

3£t>

RELD5

ROCM

TAI4KI iL. -J

IMP

PLOT

-4-

Ill. Proposed BipgasPlant

Baseline Design and Operation

We studied various digester designs and decided on a complete mix meso-philic digester, Previous work has shown digesters operating in thismode to have decided advantages over other modes (1, 2). The completemix design consists of (see Figure C) an influent conditioning tank,a heat exchanger, a main digesting tank, a gas recirculating mixer andheater, an effluent lagoon, gas storage tanks5 pumps, compressor, andfilters.

The raw manure will be deposited into the influent tank from three differentsources:

1) 12,000 Ibs/day of chicken manure trucked in from a neighboringfarm;

2) 20,800 Ibs/day of cow manure washed down from the lower shed inthe dairy;

3) 95800 Ibs/day of cow manure tractor scraped from the upper shed.

We plan to utilize the existing manure holding tank located just north ofthe lower loafing shed. This tank holds 38,000 gallons, or about, threedays of influent. The tank will be screened to prevent large objectsfrom entering the system.

At present levels of wash-down, approximately 9,648 gallons of water areused, and the mixed influent slurry contains 6.8% total solids. Thisis reported to be a minimum for proper functioning (1). The baselinedesign requires the influent slurry to contain 10% total solids whichwill force the. dairy to cut down the amount of water used to 4,922gallons/day.

The slurry will be pumped from the influent tank through an influent/effluent heat exchanger to recover effluent heat. A heat exchanger ofthis type x^as included in the Monroe State Dair}? Farm system but hasfailed to function successfully in three years of operation (1 , 4) .We feel that a heat exchanger for such viscous material can operatesuccessfully if properly designed (4).

Preheated influent slurry will be continuously fed into the main digestingtank at a. loading rate of ,31 Ibs of V,S./ft -day. The digesting slurrywill be mixed and heated to 95°F by recirculating biogas. The recircu-lating biogas will be heated by a heat exchanger which will operate atapproximately 60% efficiency. The main digesting tank will be locatedjust west of the lower loafing shed to minimize pipe length and cost.

The digested effluent will be pumped to a lagoon to insure final digestionand then deposited on the on-site corn field. The yield is 4,968 Ibsof high grade effluent fertilizer per day.

—5—

(Lower Loafing Shed) 20,880*1 bs/day total manure

,,. _, ,, 300 cows- (Upper Shed) 9j84Q ]bs/day

,. , , > 40,000 chickens-(Additional) or 125o00 lbs/day

Influent Tank

Total Ibs/day83,783

Total lbs/day T.S.8,378.3

Total cu.ft./day1,424

Lagoon

Influent

~>Effluent Flow80,360 Ibs/day

Bio-Gas -26,185 ft /day

Digesting Tank

12 Day Retention

127,824 gal

Compressor/Filter

Bio-Gas Storage1000 GallonPropane Tanks

30% for Heating(3.12 x 106 BTU/day)

HeatExchangerBurner)

HeatedBio-Gas

for Mixing

Low GradeHeat

57%. forReplacementof'PresentSystem

(9.3 x 106 BTU/day)Present Use

The resulting biogas will be piped through a H2S filter to obtain a lesscorrosive gas to be utilized by the pn-stte boiler. The total amountof biogas produced will be 26,185 ft" /day,. Of this the boiler willuse 14,800 ft /day.

A preliminary heat loss and energy balance shows that the heatingrequirement of the main digesting tank is 8,013 ft /day of biogas;thus an excess of 3,372 ft /day of biogas is produced. This excessbiogas will be stored in standard 1,000 gallon propane tanks at apressure of 240 psi. The excess gas could be utilized by varioussystems on the farm. The nearby house could use it, for space heatingand cooking. An electrical generator could also be run with methane,but the. efficiency of such a generator is only 11-20%, and this isprobably not a good use for this methane,

Alternative Designs

The costliest item of the system is the main digesting tank, so wesearched for alternative tank designs. Concrete is a suitable tankmaterial but for the large volume required, it is not quite cost-effective.We decided on the glass-fused-to-steel tank from Washington Harvestore Co»s

since it has proven to be reliable for similar digesting applications (1. 3),

Heating and keeping the slurry at 95°F within the digesting tank willrequire 3,12 x 106 Btu/day. This is about 31% of the total biogas pro-duced at a combined boiler-heat-exchanger efficiency of 60%* It wassuggested that the slurry be heated by capturing solar energy, Thereare a number of reasons why this is not an effective approach. Firstof alls there is excess biogas available above the boiler's and digestingtank's needs. Secondly, to insure a 95° digester temperature in thewinter months requires roughly 69480 ft/- of solar collector area. Ifsolar heat were, utilized in the summer months only, a collector area of3,600 ft2 would be needed, At a cost of $15-2Q/ft/ of collector surface,the extra investment: appears to be excessive.

-7-

IV. Feasibility Results

Economics

There will be enough methane produced to replace the creamery boiler'sfuel needs which are currently costing $24,000/yr. There will be anexcess of 7.93 x 10 Btu/year which has an equivalent monetary value of$5,705/year. The fertilizer produced will have an equivalent value of$15,269/year< The process will produce a total value of $44,974/year.

The estimated capital expenditures for the proposed methane digestingsystem are itemized in Table I.

Process Analysis

The results of the feasibility study are based on data from a number ofpublications. Since this is a relatively new area of research, thereis considerable variation in the data. To compensate for the possibilityof overestimation5 we have generally extrapolated conservative data fromthe various sources,

Results of the analysis are summarized in Tables II} III and IV.

Table I

ITEM

1. Conditioning Tank

2.,Digester Tank

3. Tank Installation

4. Gas RecirculationSystem

5. Pipes and Plumbing

6. Influent - EffluentHeat Exchanger

7. Manure Pump

8. Filter

9. Safety Equipment

10. Gas Storage Tanks

11, Labor Costs

ESTIMATED COSTS FOR THE EVERGREEN DAIRY METHANE PROJECT

DESCRIPTION

38,000 gal, (concrete)

Option At 40! dia. x 15" deep (147,409 gale) Slurry-stose Tank from Washington Harvestore Co.

42* dia. steel silo top

Option B: Three 24" x 12"' x 25" deep (50,000 gal.)concrete tanks from Utility Vaults Co..

24' x 12s concrete tops

Installation costs

3%" Polyurethane Foam (R-20)

Blower and Heat Exchanger

Shell and tube eoonterflow design

WEMCO sr Mitchell

H2S Removal

Gauges, Alarms, Relief Valves

1,000 Gal., jsropans tanks providing storage of2alSO ?t.J of Bio gas per tank$1S40G per tank

Construction and Design

AExisting

$51,053Built on site

$_2_2,_ooq$73,053

COST

;$6,000

$10,000

$10,000

$4,000

$3,000

$500

$6,000

1 day storage=$9,750

2 day storage—$19,500

$15,000

Existing

$54,000

$ 7,500

$12., OOP$73,500

$6,000

$10S000

$12,000

$4,000

$3,000

$500

$6,000

1 day storage1*5

$9,7502 day storage=$195500

$15,000

Total cost with one day storage

Total cost with two day storage

$137,303

$147,053

$139,750

$149,500

Table 11= MANURE AM) BIOGAS PRODUCTION AT THE EVERGREEN DAIRY

Lower Shed Cows Upper Shed Cows Chickens

Raw Manure (1)

No. of Animals (7)

Raw Manure (1)

Raw Manure,

Weight of Animal s(7«)

58 Ibs /day -cow

360 cows

20,880 Ibs/day

,017 ft3/lb

700 Ibs3

% H20 of Manure (7)

Ibs of Total Solids

Ibs of H?0

% Fixed Solids ofT.S. (2)

% V,S; Of T,S,

Biogas Production

CH, Production4

Energy Yield

Biogas (8)

Biogas Composi-tion (5, 6)

88%

2,505.5 Ibs/day

18,374,4 Ibs/day

17

83

7,516,5 ft3/day

4,885.7 ft3/day

4,89 x 106 Btu/day

3,0 ft3/lb T.S,

65% CH.4

32.8 Ibs/day-cow

300 cows

9,840 Ibs/day

.017 ft3/ib

400 Ibs

83%

1,672.8 Ibs/day

8,167,2 Ibs/day

17

83

5,018.4 ft.3/day

3,262 ft.3/day

3.26 x 106 Btu/day

3,0 ft3/lb T.S,

65% CH.4

12,000 Ibs/day

,017 ft3/ib.

65%

4,200 Ibs/day

7,800 Ibs/day

35

65

13,650 ft3/day

8,163 ft3 /day

8,16 x 106 Btu/day

3.25 ft3/lb T.S.

59.8% CH4

Daily_jrotals

Ibs of Manure - 42,720 (19% Total Solids)Ibs of Total Solids - 8,378.3Ibs of H O - 34,341,7f t3 of Biogas - 26,185ft3 of CH. •- 16,310,7Btu * s 16.3 x 10

fa

-10-

Table III. DIGESTER SIZE ANALYSIS

At 10% T0S, (Baseline Design): 83,783 Ibs of slurry/day1S424 ft3/day10,652 gal/day

Digester Size

Digester Size

V . S , Reduction (1)

10 Day Retention

14,240 ft3

106,520 gal

51%

12 Daj_Re_tentior

17,088 ft3

127,824 gal

55%

i 15 Day Ref.er

215360 ft3

159,780 gal

58%

V.S. in EffluentT.S. in EffluentH O in EffluentEffluent Total

2,790 Ibs/day4,968.3 Ibs/day75,392 Ibs/day80,360,3 Ibs/day

At 608% Total Solids; 123,209 Ibs/day2,094,5 ft3/day15,499,7 gal/day

Digester Size

Digester Size

V.S. Reduction

10 Day_ Retention

20,945 f t3

154,997 gal

n 51%

12- 2§zJ ££SSJ-i2]

25 5 134 ft3

185,996 gal

55%

15 Day Retention

31,417.5 ft3

232,495.5 gal

58%

-11-

Table IV. FERTILIZER PROPERTIES AND PRODUCTION (4, 1, 8)

Carbon/Nitrogen Ratio -25:1 Cow

8:1 Chicken

Ibs of Organic Nitrogen Available/Ib Raw Manure

Volatile Solid Reduction

Value of Effluent Fertilizer($760/ton of amoniated nitrogen)

Cows

.003

55%

$7,030/year

Chicken

,009

$8,239/year

TOTAL $15s269/year

-12-

REFERENCES

1. "Process Feasibility Study: The Anaerobic Digestion of Dairy CowManure at the State Reformatory Honor Farm., Monroes Washington,"

2. "Methane Digesters for Fuel Gas and Fertilizer, The New Alchemy Insti-tute."

3. "Operation of a 50,000 Gallon Anaerobic Digester at the State HonorFarm Dairy Monroe, Washington.," Final Report Contract: EG-77~C-06~1016, The Ecotope Group, July 1, 1978.

4. Private discussions with Dr. Jacob Bt, Romero of The Evergreen StateCollege, Applied Sciences.

5- Other Homes and Garbage, Designs for Self~Sufficient Living; SierraClub Bookss 1975."

6. "Engineering Feasibility of Fuels From Biomass Utilizing Dairy FarmResidue," Rolf T. Skrinde, Ph.D.s Tracey and Brunstrom Company, ContractNumber: ET-78-X-01-2404-Q, July 1, 1978.

7. Data gathered from the Evergreen Dairy.

8. Conservative extrapolation from various references.

-13-