key elements of biogas energy systems anaerobic digesters · brian gannon, biogas energy systems...

2005 Biogas Energy Systems www.biogas-energy.com 1

Key Elements of Biogas Energy Systems Anaerobic Digesters Brian Gannon, Biogas Energy Systems [email protected] This document describes how Biogas Energy Systems anaerobic digesters create system-

wide operational efficiencies in energy production and operational costs. While the

amount of methane that can be produced from a given feedstock is relatively fixed,

system-wide facility design can optimize methane production and power generation.

Redundancy, gas storage, flexibility, disaster prevention, multiple feed stocks: these

features and more give Biogas Energy Systems the ability to produce more energy from a

given substrate.

An “apples to apples” comparison of digester technologies is problematic since each

project has variables that may also change over time. Ultimately, the decision of which

technology to use can be made by examining the effectiveness of existing systems. This

document examines these issues and outlines the reasons why Biogas Energy Systems

digesters provide superior value and efficiency over the lifetime of a project.

In Germany, where more than two thousand anaerobic digesters operate, biogas

production has undergone decades of continual quality improvement. Since German

farmers purchase digesters for energy production, they demand the highest efficiencies.

Since they operate their digesters themselves, low-cost maintenance and operation is

crucial. Biogas Energy Systems’ technology meets these requirements and consequently

has a two-year waiting list in Europe. That waiting list does not apply to North America.

Biogas Energy Systems is dedicated to bringing mature anaerobic digestion technology to

North America and to achieving European levels of biogas production.

Vir Clar Farm, Fond du Lac, Wisconsin


Experience and Performance with Anaerobic Digestion Biogas Energy Systems’ technology partner, Biogas Nord, has built more than 200

digesters in over 90 facilities around the world, and currently completes two digesters

each week. Four digesters have been built in the US using this technology.

In the past nine months Biogas Nord built more digesters than all US developers

combined ever have. Biogas Nord will build more digesters in September 2005 (10) than

some developers have ever built. Our customers benefit directly from this experience

through fast development time, expert advice and high energy production efficiencies.

Biogas Nord technology has been improved continuously for over a decade, spurred by

the price of power in Germany and the drive to be as productive and cost efficient as

possible. Biogas Nord has never had a failed AD project and is often hired as a

subcontractor for the largest construction companies in Europe.

Biogas Nord digester technology has had flawless operations for years and is seen as the

gold standard in Europe. Ten-year-old digesters run perfectly and are prompting their

owners to expand operations by adding digesters to their facilities.

For a list of completed digester projects, see References at www.biogas-energy.com.

Energy Production Efficiency The anaerobic digester industry uses a cow/kW ratio to portray power generation

efficiency, but this measure has several shortcomings. First, methane production varies

dramatically depending on system downtime, so technologies that prevent or quickly

recover from disaster have a clear advantage. Second, by adding other substrates to

manure, far superior methane production is achieved. In addition, various substrates have

different methane production capacity (see chart below).

Key questions for energy production, with Biogas Energy Systems answers in italics:

- Can the digesters accept multiple feed sources? Yes

- What is the retention time? Depends on customer’s need

- What is the quality of the biogas? Extremely low H2S

- Is gas storage built into they facility? Yes

- Is redundancy and flexibility built into the facility? Yes

- How are problems prevented? See section below

- When a system failure occurs, how long does it take to fix it and get back up and

running? Within hours or days (not weeks), depending on the issue


Increased methane production from multiple substrates A key element to maximizing methane production is to add multiple substrates to the

digesters. Manure has low energy content since cows have already digested the substrate.

As complete & continuous mix anaerobic digestion technology, Biogas Energy Systems

digesters are extremely effective at treating various high-energy substrates. Biogas

Energy Systems digesters accept substrates other than manure, from grease to corn silage,

without any problems. Even mixed food waste can be treated.

0 100 200 300 400 500 600 700 800 900 1000

Cow manure

Pig manure

Potato waste

Chicken manure

Brewery waste

Green clippings

Grass silage

Corn silage

Food scraps

Bakery waste

Fats & Grease

m3 biogas production/ton

Biogas Energy Systems has a proven track record and best practices to enable customers

to successfully produce the maximum amount of methane from their investment.

Typically, 10-40% of digester volume may be used for substrates other than manure. The

digesters run perfectly on manure alone, but with such a dramatic effect on methane

production, customers almost always add other substrates.

Plug flow and covered lagoon digesters are unable to efficiently digest these materials,

and consequently haven’t been built in Europe in a decade.

In addition to increased methane production, multiple substrates provide waste disposal

“tipping” fees. The digester in Ireland makes most of its revenue from tipping fees for

treating food processing waste, restaurant kitchen waste, expired foods, grease, and more.

Biogas Energy Systems digesters successfully treat all of these substrates.

961

714

265

190

185

175

120

80

39

30

25


Biogas Energy Systems digesters treat a wide variety of wastes due to several factors:

- Proprietary technology significantly reduces hydrogen sulphide in biogas

- Agitation of substrates promotes digestion and prevents surface foam or crust

- Treatment in two or more tanks extracts the maximum amount of methane and

reduces pathogens to near zero

- The ability to control timing and quantity when adding substrates prevents

“shocking” the process

- Experience won from years of operation provides optimized methods of operation

- Monitoring devices and practical methods for digesting multiple substrates

prevent issues and greatly facilitate disaster recovery

Retention time increases methane production and pathogen treatment A critical factor in methane production is the amount of time the substrates spend in the

digesters. Too short retention time means an inefficient extraction of methane, so full

revenue is not realized. Too long retention time and too much was spent on surplus

capacity or not enough substrate is being added to maximize revenue.

Biogas Energy Systems plans digester retention time to get the maximum revenue with

the most appropriate capital costs. Once the facility is built, however, the retention time

can be changed as needed without affecting operations. The operator can change the

amount of substrate added, or add or shut down digesters. The operator customizes and

optimizes the system over time to achieve maximum efficiencies unique to that facility.

With longer retention time comes improved pathogen treatment. The Wisconsin digester,

designed with expansion in mind, has a 38-day retention time. Lab tests performed on

solids coming out of the digester detected zero pathogens. The farmer sells the solids as

cow stall bedding to neighboring farms and uses it for his own cows as well.

Cost of systems Just as the cows/kW ratio isn’t helpful for describing energy production, a cost per cow

figure is inadequate due to the variables involved. If a 1,000 cow Biogas Energy Systems

digester also takes 10% grease waste, the enormous increase in methane production more

than justifies the slight increase in capital costs (for reception tank & pump).

A more useful method to estimate cost is to determine all possible substrates for a

particular project, which will determine capital costs as well as revenue from energy

production and tipping fees. Then calculate power generation rates as well as downtime


estimates. In this way a lifetime financial model can be created to give a better picture

than a simple dollar-per-cow capital cost.

Based on available information, the capital costs of Biogas Energy Systems digesters are

comparable to other vendors. If gas storage and gas cleaning equipment is added to our

competitors’ cost, then Biogas Energy Systems is clearly superior. Looking at revenue

from multiple substrates and avoided downtime, Biogas Energy Systems has a distinct

advantage.

Operational costs Since each site is unique and operators have their own priorities and methods of working

with their farms and digesters, operational costs vary among facilities.

If only manure is added to the digester and the operator does not maintain a CHP unit or

gas processing equipment, the digesters require 15 minutes a day for monitoring. For

example, dairies like Vir Clar in Wisconsin automate pumping from the scrape manure

pit into the digester, and the substrate then flows via gravity through the digesters all the

way to the separator. Liquids are automatically pumped to a storage tank for land

spreading. Solids are automatically piled, so there is no human interaction with the

system (besides monitoring) until the solids are hauled away. By integrating the digesters

into farm operations, minimal maintenance and operational work is required.

Many operators add other substrates to the digesters, which increases monitoring

requirements to two or three times per day and may add some extra work.

Over the lifetime of a digester, the only equipment that may need maintenance or

replacement are the agitators or the roof. Since the agitators run only for 5 minutes an

hour, they have an expected lifespan of 8-10 years. The roof is estimated to last for 10 to

20 years. Separators, pumps, and other equipment are required for standard manure

management practices without digesters.

The main operation costs for Biogas Energy Systems owners involve the combined heat

and power unit or gas processing equipment. These must be maintained, and therefore

have costs associated. The digesters themselves, however, require little maintenance

other than daily monitoring.

It cannot be stated often enough that avoided downtime is a critical element in the

operations of a facility. Simply put, avoiding downtime and eliminating flaring cuts costs

and increases revenues. Biogas Energy Systems facilities are built with that in mind.


Gas quality and H2S treatment Biogas produced by Biogas Energy Systems digesters typically consists of approximately

60% CH2 and 40% CO2. Moisture is reduced to levels require for gas use.

Biogas contains hydrogen sulphide that must be removed as much as possible before

reaching the gas processing equipment. Some digester vendors produce biogas with

1000-3000 PPM H2S which causes severe problems with the gas processing equipment.

Biogas Energy Systems builds hydrogen sulphide cleaning technology into the digesters

as standard equipment, and produces biogas with 100-250 PPM H2S. For farms adding

substrates with very high sulphur content, additional gas cleaning equipment is available.

The hydrogen sulphide issue is a critical factor for technologies that use the biogas. If the

H2S levels are too high, damage to gas treatment equipment is severe and costly. By

using Biogas Energy Systems technology, this is not an issue.

Biogas may be converted to energy in several ways. Burning it in a Combined Heat and

Power unit generates electricity and heat. It may also be converted into Liquid Natural

Gas or compressed. The method used depends on capital costs and the price the energy

can earn.

Gas storage increases overall efficiency Gas storage is built into the roofing system, so no extra equipment or maintenance is

required. Depending on the substrates and their corresponding biogas production rates,

the gas storage can hold 10 hours of biogas or more.

By storing biogas while performing routine maintenance on gas processing equipment, no

biogas is wasted. Since the roof and gas store can be opened and closed in minutes,

repairs within the digester are quick and easy. Over the lifetime of a project, this ability to

store gas and still have instant access to the tanks is a significant efficiency factor. Instead

of shutting down operations for hours, days or even weeks, operators can avoid stoppage

or limit it to a few minutes. Every minute of gas storage is revenue.

The roofing system acts as a shell and has withstood harsh Northern European climates

for a decade. A small air pump keeps its form and maintains air pressure on the gas store.

Weatherproof outer roof Gas store within the outer roof


Redundancy and flexibility of substrate management adds efficiency Having one digester or one way to add substrate to a digester leaves little room for

optimization or disaster prevention and recovery. Without redundancy or flexibility in

substrate treatment, methane production must cease while repairs are made, losing money

each minute the process is down. For farmers who rely on manure management plans,

this can also mean costly fines.

Biogas Energy Systems digester facilities typically contain two or more digesters piped

together in every possible configuration to give operators total control of substrate flow

through the system. On-the-fly customization lets the operator maximize efficiency and

prevent/recover from disasters. By avoiding problems, efficiencies are realized.

Case 1: Two digesters running in series This is the standard two-phase facility built by Biogas Energy Systems. Depending on the sizes of the digesters and the amount of material put in, total retention time is 28-36 days. Case 2: Two digesters running parallel Two digesters may also be run in parallel if need be. Changing between series and parallel is accomplished by opening or closing a few valves in a matter of minutes. Case 3: Second digester is down for repair or bacteria failure If a digester is taken offline for maintenance or goes offline due to problems with the bacteria, the substrate can simply be re-routed straight to output so operations can continue. In addition, healthy bacteria can be added from the healthy tank (green arrow) to prevent disasters or to expedite recovery.

Case 4: First digester is down for repair or bacteria failure See case 3.

Case 5: Three or more digesters Three or more digesters use the same principles as cases 1-4, so the operator has complete control of substrate flow through the system, i.e. in series, in parallel, two parallel and both flowing into the third, etc. Changes to the flow configuration are made in minutes by opening and closing several valves. Digester facilities can expand over time simply by adding tanks.


Disaster prevention and recovery lowers costs, increases revenue Digester downtime causes loss of revenue, additional work, and higher costs. Design

elements developed over the last decade enable Biogas Energy Systems technology to

prevent issues from causing system degradation or failure. Farmers don’t have time or

expertise to devote to complex, error prone technology, so Biogas Energy Systems builds

digesters with simplicity in mind. Improvements or repairs can be done by the

farmer/operator, and soon the owner knows the digester better than the builder. Over the

lifetime of a project, reduced downtime translates into significant energy production

efficiencies for Biogas Energy Systems digesters. Any loss of methane production for

any length of time is money lost, and the following elements prevent such problems.

- Web-based computer monitoring of gas production enables operators to see

functions from anywhere in the world and make changes as needed. Alarms

automatically phone the digester operator and provide a message of any issue that

arises so the necessary steps can me taken.

- Windows into the digesters (at left of

photo) give crucial visual status of

the contents. Any unhealthy

developments within the tank such as

buildup of foam or crust can be

quickly identified and dealt with

before they become a real issue.1

Changing the height and/or direction

of agitators (center of photo) fixes

these issues and prevents a disaster.

- Since digester roofs can be opened easily to access any equipment within the

digester, maintenance doesn’t affect operations. If an agitator needs attention, fold

back the roof, remove the agitator and close the roof within minutes.

- Gas production sensors automatically shut off gas processing or CHP equipment

to prevent damage. The operator configures the controls so that the gas processing

equipment can be automatically turned down if gas production drops. If gas

1 This is a critical problem for concrete-roofed digesters that have no visual access within. There have been cases of a buildup of foam within digesters that caused the roof to break its seal and stop operations for weeks. Without visual monitoring within the digester, it’s impossible to know a problem exists.


production stops altogether, the gas processing equipment is turned off to prevent

system damage.

- Using proprietary technology, H2S is automatically removed from the biogas to

100-250PPM2; well within the accepted level for most gas processing equipment.

- By taking samples of pH at any time from the well-mixed digester contents,

operators can tell when to add additional substrates and in what quantities. For

example, if the pH starts to decline after adding a certain substrate, adding manure

improves the process and prevents problems from escalating.

- Accidental over-input of substrate has no long-term ill effects; it just pops the roof

off. To fix it, simply drain substrate to the proper level and re-attach the roof to

regain the seal. For concrete roofed digesters, an overflow like this means weeks

of downtime to re-seal the roof.

- Typically, only one pump is used to operate the facility. Gravity forces substrate

between digesters and out of the system. Fewer mechanical parts mean lower

costs, lower parasitic load and fewer repairs.

- Since all digesters are connected with

pipes, bacteria from a functioning

digester can be added to “sick”

digesters to prevent degradation or

cessation of biological processes. The

manifold in the photo directs substrates

through the facility and can be

reconfigured manually in minutes.

- Mesophilic digesters are less complicated and more easily maintained than

thermophilic digesters, and have a wider range of acceptable temperature for

substrate treatment. This translates into lower capital and operational costs, less

downtime, and lower parasitic load.

- Equipment used to construct the facility is readily available and easily maintained

by the operator. Biogas Energy Systems provides support.

2 Levels may vary depending on substrate.


Expandability reduces initial investment and can be done easily Even with adequate planning, a digester’s throughput capacity may be reached well

within the lifetime of the facility, especially as the operator increases his success. As the

farmer expands operations more digester capacity is required.

Rather than excavating around an underground digester and knocking down a wall to

expand it, Biogas Energy System’s modular design enables the owner to simply add more

digesters and expand capacity to any size in 3-4 weeks.

Expansion is completed without interruption of existing digesters’ operations.

This enables owners to install minimal capacity initially and expand as needed, rather

than building for future capacity and having that capital cost go unused perhaps for years.

Low parasitic load reduces costs Digesters are heated to foster bacteriological action. Any biogas used for heating is not

adding to the revenue stream, so the parasitic load is kept to a minimum. With insulation,

a circular tank, and heating pipes embedded in the floor and walls promoting even,

permeating heat, Biogas Energy Systems digesters are extremely energy efficient.

Ambient temperature and the temperature of

the substrate as it is added to the digesters

dictates the amount of heat required, so it’s

difficult to give a standard parasitic load.

As an example of the efficiency of Biogas

Energy Systems technology, the two

Wisconsin digesters, each 2,500m3, were

brought to proper temperature in seven days

during sub-zero temperatures.

Since the heating pipes are typically

embedded within the walls of the digester,

(seen in photo) they will last for the lifetime

of the digester. Other vendors hang steel

heating pipe within the digester, adding a

risk that they will need replacement after

several years of operation.


Combined Heat and Power Unit For those customers who want to generate electricity and sell surplus power to the grid,

Biogas Energy Systems installs Combined Heat and Power (CHP) units.

Other gas processing technology may also be used, such as gas compression or

production of liquefied natural gas, and Biogas Energy Systems helps customers identify

those technology providers. Ultimately, the choice of technology depends on capital costs

and the revenue each can generate.

Biogas Energy Systems installs several brands of CHP unit, including Seva, 2G,

Jenbacher, Caterpillar, or others, depending on customer requirements.

The CHP unit is typically shipped to the sight in a sound-insulated container, and simply

hooked into the system.

Since the equipment is extremely sensitive to hydrogen sulphide in the biogas, H2S is

reduced to acceptable levels using proprietary Biogas Energy Systems technology. This

increases CHP efficiency by reducing maintenance, preventing downtime, and enhancing

energy production.

Equipment built into the digester facility also extracts moisture from the biogas, thereby

greatly reducing wear and tear on the CHP machinery.

Heat generated by the CHP unit is used by the digesters, and ample surplus heat is also

available for heating of barns, buildings, parlor water, greenhouses, etc. or for additional,

optional pasteurization of substrate.

Depending on the agreement made with local power utilities, electricity generated may be

net metered, fed directly to the grid, or handled in another way.

Container housing the CHP unit CHP unit within the container


Fiber quality produces other sources of revenue

The Wisconsin farmer separates solids from the effluent and uses it as bedding for his

1100 cows, thereby eliminating bedding costs. He also sells it as bedding to surrounding

farms. Recent lab analysis showed zero pathogens in his digester’s solids.

Two universities are studying solids from the Wisconsin digester to develop soil

amendment or peat moss replacement. There is reason to plan for solids getting $12-

$25/yd3 from compost customers or greenhouses, which adds significantly to the

facility’s bottom line.

Anaerobic digestion for dairies In the future, anaerobic digestion will be a standard part of dairy operations.

- Eliminates odors

- Enables expansion of herd without acquiring land

- Reduces or eliminates pathogens from waste stream

- Improves nutrient management

- Generates revenue from methane production & greenhouse gas emissions offsets

- Generates revenue from compost or bedding sales

- Offsets power costs

- Low cost, low maintenance, easy integration

- Prevents regulatory penalties for waste treatment

Cow sleeping in bedding material from digester. Note clean udder and underbelly: manure on hoof is from lane, not stall.

Solids are separated and used for bedding or compost. Liquid nutrients are field-spread.


Conclusion Biogas Energy Systems welcomes the opportunity to provide estimates on projects or

perform feasibility analyses. Biogas production rates, facility costs and operational costs

can be calculated based upon specific project factors.

We welcome questions about our technology and are delighted to offer tours of our

facilities in Wisconsin.

Please contact us for specific performance data on individual facilities.

Attendees of 2005 BioCycle conference visiting Vir Clar farm

Vir Clar farm with digesters at left

key elements of biogas energy systems anaerobic digesters · brian gannon, biogas energy systems...

Documents