[Stoves] combusting Coffee Pulp/Cherry

Fri Feb 10 19:30:36 CST 2012

Paul

I build a proto-type Cremasco Bioheater for the Pinhalense Group in Brazil
where we successfully combusted freshly processed coffee pulp that contained
a moisture content of about 80% without
any smoke emissions. See below;
Cheers
Frank Scott
**********************

The Cremasco Bioheater for the Coffee Processing Industry

The Cremasco Bioheater gets its name from its inventor, Father Dominic
Cremasco, who in the 1960s design a furnace to completely combust (at high
combustion temperatures) low-grade wet biomass materials that normally would
not be considered fuel. While numerous Cremasco Bioheaters have successfully
operated since the mid-1980s, only recently has there been a focused
engineering effort to match the process with specific commercial
applications. A feasibility study by The Rocky Mountain Process Group in the
United States concluded that the drying of wet coffee beans using heat
produced from the combustion of coffee pulp in a bioheater is a viable
application of this technology. The coffee processing application
simultaneously addresses an environmental problem (pulp waste disposal) and
offers the economic and environmental benefit of reduced or eliminated
fossil fuel and wood consumption.

HOW IT WORKS

Wet feed materials like coffee pulp can be successfully processed because
the bioheater is designed to first dry and partially burn the biomass feed
material in a primary chamber followed by complete combustion of the gases
and residual char material in a secondary chamber. Biomass is fed either
manually or automatically to the bioheater and ash is withdrawn from the
bottom of the unit. From such wet fuels, the bioheater has demonstrated that
it can sustain combustion temperatures of 1,000ºC to 1,200ºC with no visible
emissions to the atmosphere. Heat in the flue gas is transferred by a heat
exchanger to flowing air or water for space or process heating such as
coffee bean drying.

WHY COFFEE PROCESSING

Dried green coffee beans represent only about 16% of the weight of ripe
coffee cherries, resulting in a large amount of pulp waste with limited use
in other applications. Coffee pulp waste is a pollutant that is banned from
some waterways but in some regions continues to be dumped in rivers. In most
cases, solar drying is not completely effective. Freshly pulped, fermented,
and washed parchment coffee has a moisture content of about 55% by weight
and must be reduced to under 11% for long term storage and roasting. At this
moisture content, the parchment husk prevents deterioration of the dry
coffee beans. Optimal temperatures for mechanical air drying of coffee beans
are in the range of 45 to 55ºC and the drying process typically takes 24 to
36 hours. The beans are subject to a continual flow of warm air during which
time they undergo distinct changes in color, hardness, and chemical
composition.

BENEFIT TO COFFEE GROWERS

The Cremasco Bioheater consumes coffee pulp as fuel to generate heat for
drying wet green coffee beans. This approach offers the following
significant advantages and no obvious technical drawbacks:

· the potential for the solution of multiple environmental
problems.(consumption of polluting coffee pulp as fuel, and reduction in
deforestation for fuel wood),

· contributes to the concept of sustainable communities,

· encompasses an enormous international market,

· reduces risks relating to coffee spoilage (more rapid drying than solar
drying),

· the ash produced from the Bioheater can be used as fertilizer to return
minerals to the soil for coffee growing, and 

· dry coffee beans can be sold for many times the value of wet beans, thus
the farmer gains added sales flexibility due to greatly increased storage
time.

PROPOSED COFFEE DRYER

The Propsed Cremasco Coffee Dryer is based on drying a 1,000 kg batch of wet
green beans in a 32 hour period. The wet pulp feed rate to the Bioheater is
86.1 lb/h (wet basis) and assumes 65 wt% moisture in the pulp. Other key
assumptions include a wet pulp / dry green coffee mass ratio = 2.5, wet
green coffee moisture content = 55 wt%, dry green coffee moisture content =
10 wt%, ash content of bone dry pulp = 5 wt%, bone dry pulp heat of
combustion = 7,333 Btu/lb.

<outbind://94-00000000BEEAD2195EADBF43A52C62FF83E7F8D3E44A3300/cid:446265908
@01072011-1683> 

Figure 1: Cremasco Bioheater Coffee Drying Process

Figure 1 illustrates the major components of a simple, small Cremasco
Bioheater Coffee Bean Drying System. This system has a capacity of 1,000 kg
of wet coffee beans per batch. Smaller and larger systems can be designed
for a range of coffee bean processing rates. 

Other potential applications for the Cremasco Bioheater include the coconut
oil, palm oil, citronella oil, and domestic farm animal industries.

Our current proposal is to optimise the bioheater for application in the
coffee industry. For further information contact Frank Scott on (61-8) 9474
1026 or by email at  <mailto:franks at q-net.net.au> franks at q-net.net.au, 

Mass and Energy Balance for the Cremasco Bioheater: 

Coffee Pulp Processing 

The following tables provide the results of a mass and energy balance
spreadsheet model for the Cremasco Bioheater. The model assumes that coffee
pulp with a moisture content of 65 wt% is the only biomass feed to the
Bioheater. The heat generated by the combustion of coffee pulp is then used
to heat a separate air stream, which can be used for drying green coffee
beans. This high moisture content for coffee pulp is realistic and
represents the high end or essentially a “worst case” moisture content for
biomass in general. 

As with any process model, key assumptions were required and are summarized
in Table 1. 

Table 1. Major Assumptions used In Mass and Energy Balance Model

Biomass (coffee pulp) feed rate 

100 kg/h

Biomass (coffee pulp) heat of combustion (dry basis)

4,073.9 kcal/kg

Biomass moisture content (wet basis)

65 wt%

Biomass ultimate analysis (dry basis) (wt%)

Carbon

43.400

Hydrogen

7.165

Oxygen

41.495

Nitrogen

2.940

Ash

5.000

Base temperature for thermodynamic calculations

25 0C

Temperature of inlet air streams

25 0C

Biomass feed internal preheat temperature

65.5 0C

Combustion air internal preheat temperature

260 0C

Bioheater total surface heat loss

18,905 kJ/h

Flue Gas to Atmosphere temperature

107.2 0C

Temperature of drying air to drying process

55 0C

In the model, combustion air (excess air above stoichiometric) is adjusted
to achieve a minimum 3 % by volume oxygen in the flue gas, simply as a
general guideline for good combustion practice. The results show that even
with 65 wt% moisture in the coffee pulp feed, a Bioheater flue gas
temperature of 979 0C can be achieved. Lower moisture content feed will
allow Bioheater operation at higher temperatures and/or higher oxygen
concentrations in the flue gas. The optimum temperature is that which
provides complete combustion of hydrocarbons in the flue gas. For a given
biomass composition, biomass feed rate, and air feed rate, preheating of
feed and combustion air only affects the combustion temperature, and has no
effect on the available sensible heat in the flue gas.

The summary energy balance around the Bioheater only is shown in Table 2.

Table 2. Energy Balance Summary for the Cremasco Bioheater

Energy Inputs

kJ/h

Biomass Combustion Energy

567,107

Air Preheat

61,639

Feed Preheat

12,903

Total Input

641,649

Energy Outputs

kJ/h

Latent Heat of Vaporization of H2O

158,811

Surface Heat Loss

18,905

Flue Gas Sensible Heat

462,470

Ash Sensible Heat

1,398

Total Output

641,584

Energy Balance Closure =

99.9899%

Fig. 1 and Table 3 provide a Flow Diagram and corresponding Mass and Energy
Balance for the Cremasco Bioheater. In the diagram (Fig. 1), the Bioheater
internal heat transfer pathways are shown schematically as brown lines and
are not intended to reflect the actual physical arrangement of the
Bioheater. 

Direct transfer of heat from the flue gas to drying air using a flue gas
heat exchanger is assumed in this example. Results show that more than
enough heat is available in the flue gas from the combustion of coffee pulp
to dry green coffee beans from the pulping operation. Based on literature
surveys, it appears that for optimum air drying of a batch of green coffee
beans (from 55% moisture to 10% moisture), the operation should take about
32 hours with a heated air stream temperature of 55 0C. Approximately 1.5 kg
of wet green coffee beans are produced per kg of wet coffee pulp, so the wet
green bean production rate would be 150 kg/h. The starting green bean batch
size would be (32 h)(150 kg/h) = 4,800 kg batch. To dry the wet green beans
from 55% to10% moisture, 74.98 kg/h H2O must be evaporated. The total heat
required for the drying would be approximately 197,813 kJ/h. 

In this example, the Cremasco Bioheater processing 100 kg/h of coffee pulp
containing 65 wt% moisture will produce flue gas with a gross sensible heat
content of 387,928 kJ/h. If it is assumed that the temperature of the flue
gas discharged to the atmosphere is 107 0C as in this example, the net
sensible heat available for heating air for drying is 352,330 kJ/h.
Therefore, almost twice as much heat is available from processing coffee
pulp as required to dry the wet green coffee beans. The surplus heat
(154,517 kJ/h) could be used to dry larger batches of coffee beans or for
space heating or hot water heating. 

Table 3. Mass and Energy Balance Summary for the Cremasco Bioheater (Coffee
Pulp Processing) 

  _____  

From: stoves-bounces at lists.bioenergylists.org
[mailto:stoves-bounces at lists.bioenergylists.org] On Behalf Of Paul Olivier
Sent: Saturday, February 11, 2012 5:18 AM
To: Discussion of biomass cooking stoves
Subject: Re: [Stoves] Coffee Pulp/Cherry

One of the best ways to manage wet coffee pulp waste is to ferment it.
See: http://esrla.com/pdf/landfill_07.pdf
The fermented coffee pulp is then fed to pigs.
The feces of the pig is fed to BSF larvae,
and the residue of the larvae is fed to red worms.

One of the best ways to manage dry coffee husk waste is to gasify it:
http://esrla.com/pdf/landfill_06.pdf
To prevent agglomeration of the biochar and to enhance gasification,
it is best to gasifiy the coffee husk together with some rice hulls.
I mix them 50%/50% by volume.
Simply burning coffee husks is really a bad solution,
since it gives rise to a lot of truly awful black smoke.

Thanks.
Paul Olivier
Paul A. Olivier PhD 
27C Pham Hong Thai Street
Dalat
Vietnam
Louisiana telephone: 1-337-447-4124 (rings Vietnam)
Mobile: 090-694-1573 (in Vietnam)
Skype address: Xpolivier
http://www.esrla.com/

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