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06-05-2013 SARBS 1 Maintaining a Biogas Purification System
06-05-2013 SARBS 1
Maintaining a Biogas
Purification System
06-05-2013 SARBS 2
TIPS FOR
MAINTENANCE SAVINGS
06-05-2013 SARBS 3
REVIEW OF BIOGAS
TREATMENT PROCESSES
06-05-2013 SARBS 4
1. Inlet raw gas coalescer
2. H2S Removal
− Bioscrubber
− Iron Sponge
− SulfaTreat®
06-05-2013 SARBS 5
06-05-2013 SARBS 6
06-05-2013 SARBS 7
06-05-2013 SARBS 8
3. Particulate Filter 4. Blower(s) or Compressors
5. Moisture Removal System
− Compressor
− Recirculation Pump
− Condenser
06-05-2013 SARBS 9
06-05-2013 SARBS 10
6. Water Droplet Coalescer 7. Siloxane Removal System
8. Final Particulate Filter
06-05-2013 SARBS 11
Where to look for
ways to save on
maintenance
06-05-2013 SARBS 12
Coalescers and Filters are
only a small part of the
O&M Budget, so not much
can be gained by tweaking
these.
06-05-2013 SARBS 13
Two potential areas of savings:
1) Replace “non-cleanable” filter
elements with cleanable
mesh pad type elements;
2) Possibly eliminate coalescers
ahead of iron sponge vessels.
06-05-2013 SARBS 14
Implement a preventative
maintenance program for
blowers and moisture removal
equipment. This is critical as
the equipment ages. Budget
key parts replacements.
06-05-2013 SARBS 15
As an alternative to in-house
programs, consider purchasing
a service maintenance
agreement from a 3rd party.
These are inexpensive and will
free up labor resources for
more critical plant matters.
06-05-2013 SARBS 16
So far, we have discussed
items that contribute to only
15% to 20% of the total
maintenance budget.
06-05-2013 SARBS 17
The two biggest cost items
are:
1) H2S removal media and
2) Siloxane removal media
replacement.
06-05-2013 SARBS 18
H2S removal media
replacement can be as
much as 40% to 45% of
the total maintenance
cost on a digester gas
purification system.
06-05-2013 SARBS 19
As a rule, it costs about $1.00 to
$2.50 per pound of H2S removed
from a digester gas stream (the
higher number is for SulfaTreat®).
This includes the new media,
labor, disposal and transportation
costs.
06-05-2013 SARBS 20
One pound of H2S is
equivalent to 1 MMSCF of
digester gas containing
just 11.4 ppmv of H2S.
06-05-2013 SARBS 21
The costs add up fast. A
digester gas stream with
a high siloxanes level
can cost $100’s each day
for purification.
06-05-2013 SARBS 22
Ways to save on H2S removal:
1) Keep pH of iron sponge
above 7.0.
2) Make sure there are 2
ppmv of oxygen for each
ppmv of H2S in the biogas.
06-05-2013 SARBS 23
3) Try an air scour to restore
the iron sponge effectiveness.
Oxygen will enhance the H2S
removal and extend the media
life.
06-05-2013 SARBS 24
4) Review H2S Removal
System design parameters to
determine if the proper
equipment is being used.
Some rules of thumb:
06-05-2013 SARBS 25
• Consider the use of a
bioscrubber if H2S level is
above 250 ppmv.
• Iron Sponge and SulfaTreat®
are best used if the H2S level
is 100 to 400 ppmv.
06-05-2013 SARBS 26
• If a bioscrubber can be
installed, it can reduce H2S
removal O&M costs by 75%
or more. This offers an
attractive payback on the
capital investment.
06-05-2013 SARBS 27
Siloxane removal media
replacement can be as
much as 50% to 55% of
the total maintenance
cost on a digester gas
purification system.
06-05-2013 SARBS 28
As a rule, it costs about $4.00 to
$4.50 per pound of siloxanes
removed from a digester gas
stream. This includes the new
carbon media, labor, disposal and
transportation costs.
06-05-2013 SARBS 29
One pound of siloxanes is
equivalent to 1 MMSCF of
digester gas containing
just 0.97 ppmv (970 ppbv)
of total siloxanes.
06-05-2013 SARBS 30
The costs add up fast. A
digester gas stream with
a high siloxanes level
can cost $100’s each day
for purification.
06-05-2013 SARBS 31
Ways to save on siloxanes
removal:
1) Consider a carbon exchange
service (CXS) or a carbon
recycle service (CRS). These
can save as Much as 50% of
the cost of new media and
disposal of the spent media.
06-05-2013 SARBS 32
2) Consider replacing the non-
regenerable siloxane removal
system with a regenerable
one, such as the CompHeet™
Process. This can save as
much as 75%, and has a good
payback.
06-05-2013 SARBS 33
Perform a review your
Siloxane Removal System
design parameters to
determine if a regenerable
system is a good fit. A rule of
thumb:
06-05-2013 SARBS 34
• Consider the use of a
regenerable siloxane removal
system if the total of the
siloxanes and VOCs exceeds
25 ppmv.
06-05-2013 SARBS 35
• Another area for potential
savings is in analytical tests.
Consider the use of a multi-
function in-line analyzer and
use a laboratory only for tests
it cannot perform.
06-05-2013 SARBS 36
Wrap-up and Questions
