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Biofuel processing

Maximising biogas production efficiencyThe biofuels sector, including biogas, is a fast growing industry

because it means less reliance on fossil fuels, and it is sustainable.

However, biomass is a difficult media, so has to be broken down

to allow pumping to take place efficiently and to maximize biogas

production. Harald Vogelsang explains.

Biogases are gases produced by the

biological breakdown of organic

matter in the absence of oxygen.

Such gases – mainly methane and carbon

dioxide (CO2) – are produced by anaerobic

digestion or fermentation of biodegradable

materials, which include municipal waste,

biomass, manure/sewage, green waste, and

energy crops (Figure 1).

As methane can be burned, it makes an

ideal low-cost and relatively ‘green’ sustain-

able and renewable fuel to power any

form of heat engine to generate either

mechanical or electrical power. It can also

be compressed to power vehicles. Biofuels,

such as biogases, therefore help reduce

reliance on often ‘dirty’ and increasingly

expensive fossil fuels.

Many biogas plants originally started in

Germany, because German farmers typically

had slurries they needed to be rid of – this

provided the biomass from which biogases

could be obtained. In addition, there were

biogas plants for producing power out of

various wastes, including biological waste.

Ever since the biogas boom started about

a decade ago, the demand for biogas tech-

nology has become very strong, and there

is increasing interest around the world. In

Germany, for example, there is currently a

great deal of business to be had in biogas

production, pumping and storage, which

involves, among other things, biomatter

crushing techniques and signifcant use of

pumps. Apart from the intrinsic merits of

biogas, one significant reason for this is

that biogas demand has been increasing

because of legislation. In Germany, compa-

nies are paid for any power they supply

to the grid. The legislation was changed

recently, so that electrical power produced

from biogas now obtains a high purchase

price for electricity generating companies.

It is this aspect that has helped the biogas

boom in Germany, but other countries

either have similar legislation or are likely to

have it soon.

Figure 1. Biodegradable materials include municipal waste, biomass, manure/sewage, green waste, and energy crops.

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Pump manufacturers, being often involved in

supplying large products for very big projects,

have a much more immediate feel for how

economies are doing around the world,

because they are much more international in

terms of contract placements, which are often

municipal or governmental. This feeds back

a realistic barometer of the general global

economic situation, because when money

starts to be spent on biogas or wastewater

projects, pump manufacturers know that

money is being released through various

government departments and budgets.

Biomatter preparation

Biomass is a difficult media, so has to be

broken down to allow pumping to take

place efficiently and to maximize the biogas

yield. The biomatter has to be crushed or

cut, so that fibres and biological matter

are chopped up, creating a greater surface

area that makes it easier for the bacteria to

digest the material. In addition, any heavy

objects must be removed before processing

can proceed further.

This is achieved using high performance wet

cutters and macerators having an integrated

heavy object separator. Such machines are

often similar to those used in the waste-

water treatment industry (sludge and very

dirty wastewater present similar problems),

but biogas is a much newer industry with

heavier end user involvement. Biogas

companies tend to take greater ownership

and are more involved with the plant design

from the very beginning.

Hugo Vogelsang Maschinenbau GmbH, for

example, is a leading designer and manufac-

turer of agricultural, municipal and industrial

products that are used to prepare biodegrad-

able materials for biogas production plant. The

company is also a pump manufacturer but it

focuses on the biogas and wastewater treat-

ment sectors, and on agriculture and the oil

industry. Even over the past year, the company

grew 10% despite the recession, and it has

seen years with 30 to 40% growth. As a result,

it expects good future turnover and profit.

Importantly, a significant part of this is built

upon the biogas sector.

Products for these sectors include wet cutters,

macerators and rotary lobe pumps, and

combinations of the two. The high demand

for products such as these that disintegrate

biomass and biological materials is because

they are exactly what biogas industry needs.

Biomass preparation

The crushing and macerating machines, like

Vogelsang’s RotaCut (Figure 2), solve typical

problems involving coarse and fibrous foreign

matter and foreign objects in liquid media.

The liquid media flows continuously through

the unit. Foreign objects such as stones, metal

parts, etc are separated by gravity and can

easily be removed later through a cleaning out

port. All material that floats, such as fibrous

materials, bones, wood, etc, are carried by the

flowing medium to the cutting screen where

the solids are cut up using rotating, self-sharp-

ening knives. In this way, foreign objects are

separated, while coarse and fibrous materials

are chopped up, making the liquid medium

homogeneous. The method also keeps all

foreign objects away from pipe systems,

preventing pump clogging and helping to

assure trouble-free system operation. Blockage

protection is available through the auto-

reverse function.

Four different heavy object separators are

available for different applications and media.

These are: cyclone with heavy object separator;

intake and discharge arranged in-line; the MXL

that is ideal for vehicle mounting; and the

compact XL model. Different drive systems

and hardened steel cutting screen sizes also

help customers meet varying applications.

Another way of disintegrating biological

materials is by using high voltages. The

process is extremely good at disintegrating

these, providing a greater surface area that

makes it easier for the bacteria to consume

the biomatter. The result is extra gas yield out

of the digested material – up to 18% more.

Vogelsang’s BioCrack (Figure 3) works this way,

and its other great advantage is that very little

energy is used – each system runs using just

35 W of power. This relatively new technology

also works well with macerating machines,

such as RotaCut. Typically, a rotary lobe pump

is used to flush through a RotaCut into the

BioCrack, recycling material to the digester

in exactly the right form for efficient biogas

production.

Such a system reduces the power required for

mixing – a very significant benefit, because

conventionally, mixing is energy intensive.

Several technologies from various manufac-

turers are available that provide good biomate-

rial disintegration, but the energy demand is

high, and an increasing number of end-users

are requesting greater energy savings. The

combination of RotaCut and BioCrack is ideal

for obtaining good results at very low cost.

Figure 2. Crushing and macerating machines, such as Vogelsang’s RotaCut, solve typical problems involving coarse and fibrous foreign matter and foreign objects in liquid media.

Figure 3. Vogelsang’s BioCrack uses high voltages to disintegrate biological materials. One great advantage is that very little energy is used – each system runs using just 35 W of power.

Figure 4. Vogelsang rotary lobe pumps – such as this VX230 model – are used in conjunction with biomass crushers, cutters and macerators.

Figure 5. BioCut is a combination of rotary lobe pump and the RotaCut wet shredder.

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Elastomer-coated pumps

Vogelsang rotary lobe pumps (Figure 4) are used in conjunction with

biomass crushers, cutters and macerators, sometimes in the same unit,

such as the BioCut (Figure 5), which is a combination of rotary lobe

pump and RotaCut wet shredder. These pumps can easily handle even

abrasive media, acids or liquids with high solids content.

To meet virtually any application, the pumps are available in various

materials, including grey cast iron with tungsten carbide (TC) coating,

aluminium or stainless steel, with combinations of hardened and/

or coated housing and wear components. There are also mechanical

sealing options, including as a cartridge, with duronite or SiC, and there

are various lobe materials and geometries that can be provided to suit

specifi c applications.

The advantages of this type of pump for the biogas, wastewater,

sewage treatment, recycling, drinking water supply and other sectors

are as follows:

• Changeable pumping direction

• Self-priming

• Insensitive to running dry, foreign objects and particles

• Compact design allowing reduced space requirements

• Pulsation-free lobes

• Flow rate proportional to pump speed

• Very good accessibility for maintenance and repair.

Improving maintenance

The bio industry is very demanding because of the highly diffi cult

media that systems have to contend with. Examples include sludge

and maize, which both contain much dirt, such as sand, stones and

foreign bodies. All of this has to be mixed together and pumped to

all of the bio-units. This is a very abrasive and demanding material,

and can quickly wear pumps and other equipment, so customers

are requesting that lifetimes be improved. Research and develop-

ment is ongoing into this crucial aspect.

A related aspect is ease of maintenance, which is one of the key

features for customers. Everything must be accessed very easily; it

must be possible to remove and replace worn parts quickly. ■

Figure 6. A Vogelsang rotary lobe pump showing the coated lobes.

Contact

Holger Eggert

Director of Marketing

Hugo Volgelsang Maschinenbau GmbH

Holthoge 10 - 14, D-49632

Essen Oldb, Germany

Tel: +49 5434 83 231

Email: eggert@vogelsang-gmbh.com

Web: www.vogelsang.info