Landfill & Biogas Solutions for H2S Measurement Applications0 pages

Application Note

Landfill & Biogas

Emerson Offers Landfill & Biogas Solutions
for H2S Measurement Applications
Applications
As a by-product of recycled waste and raw materials, Landfills
and Biogas facilities generate gases that can be used for multiple
purposes such as fuel for boilers, dryers and heaters, power
generators for engines and turbines, or even be supplied into a
natural gas network. Comprised primarily of methane (CH4) and
carbon dioxide (CO2), these gases may also include traces of oxygen,
nitrogen and water, and in some cases contain hydrogen sulfide
(H2S) at concentration levels of several hundred ppm.
Local power production facilities often use the processed gas from
these facilities to power the engines of the generators. Because the
combination of H2S and moisture is highly corrosive, operators use
gas analyzers to closely monitor the H2S levels in order to prevent
corrosion, which can cause costly damages to the engine.
Another common application of Landfill and Biogas usage is the
production of Biomethane, where the extraction of CO2, H2O and
H2S components allows the resulting purified gas to be injected into
natural gas grids. Even though Biomethane is purified, low levels of
H2S may still remain, and therefore local authorities often set strict
regulation limits towards its use. For example, in Europe the H2S limit
is 3.3 ppm.

Electrochemical Sensors for H2S

Rosemount Analytical offers electrochemical sensors for H2S in
three measuring ranges:
■■ 0–50 ppm
■■ 0–200 ppm
■■ 0–2,000 ppm
With Rosemount Analytical’s electrochemical cell, H2S is oxidized to
sulfuric acid (H2SO4) which produces a current proportional to the
H2S concentration. These inexpensive sensors are quite selective
and sensitive down to low ppm concentration levels, however they
require moisture and oxygen to maintain constant sensitivity,
therefore an ambient air purge cycle is implemented.
The X-STREAM Enhanced™ analyzer has an internal programmable
logic controller (PLC), which is used to control the internal valve logic
for implementation of the purge cycle. Purge and measurement
intervals are set to 10 minutes each but can be easily configured to
other field conditions.

Integrated Solution
In addition to H2S measurements at Landfill and Biogas sites, other
measurements are needed. Methane (CH4) and carbon dioxide
(CO2) are the main constituents and define the calorific value or
quality of the gas and are measured with an IR photometer. Oxygen
(O2) is a safety measurement performed with electrochemical
cells or paramagnetic detectors. These additional measurements
are done continuously in series with H2S when the H2S sensor is in
measurement mode. When the H2S sensor is in a purge cycle, it is
switched to parallel mode, relative to the active measurements.
In addition to providing continuous accurate measurement analysis,
the X-STREAM Enhanced includes built-in purge, calibration valves
and pumps, providing a complete turn-key solution ideal for Landfill
and Biogas applications.

Typical Biogas Facility