New S4000TH Hydrogen Sulfide Gas Detector with HART® Communication
Hydrogen sulfide (H2S) gas is a common product of the decomposition of dead plant and animal material. Man-made releases of H2S into the air result primarily from the production and refining of oil and natural gas as well as wastewater treatment, pulp and paper manufacturing, and food processing.
The new S4000TH Gas Detector is designed to protect people, equipment, and plants from the dangers of H2S, and features the HART communication protocol for ease of field communications. HART is a field-proven instrumentation communications protocol that provides two-way digital communication without disturbing the integrity of the 4-20 mA analog output. HART permits several variables, parameters, device configuration, and device diagnostics to be transmitted digitally at the same time as the analog signal. Unlike other digital communication methods, HART is backward compatible with the installed base of instrumentation in use today.
Human Health Effects from Exposure to H2S
Hydrogen sulfide is a flammable, odorless, and highly toxic gas with a characteristic odor of rotten eggs. Although about half of the population can smell the gas at concentrations below 8 parts per billion (ppb), concentrations above 150 ppb quickly impair the sense of smell. Most effects to humans occur from inhalation, although H2S can also cause eye irritation. Exposure to lower concentrations can produce irritation, shortness of breath, and fluid in the lungs. Breathing high concentrations (≥ 1,000 parts per million) results in immediate collapse, respiratory paralysis, followed by death. The OSHA Permissible Exposure Limit (PEL) for General Industry of the gas is 20 ppm (ceiling).
Detecting H2S Gas Releases
Escapes of H2S gas, whether as routine emissions or accidents, have the potential to produce harm to people and facilities, even beyond those found in proximity to a leak source. Some common problem areas and gas monitoring applications are listed below:
Crude Oil Tank Storage
Storage tank farms for “sour” crude oil require continuous monitoring for gas leaks. In addition to the tanks, common leak sources include pipes and valves.
Remote Oil and Gas Well Sites
Remote automated oil and gas well production sites require protection against H2S gas leaks in and around the site. Common monitoring locations include well heads, flare stacks and storage tanks.
Oil and Gas Drilling Sites
Leaks, such as blowouts in oil drilling applications, release large quantities of H2S gas into areas around the site. Appropriate locations for gas monitoring are the driller stand, bell nipple, shale shaker, mud-return receiver tank, and operator’s station.
H2S Sludge Dewatering
Sludge from waste treatment facilities may contain H2S and methane gas as well. The sludge is transported through a spiral conveyor into the dewater system where the water is removed.
To prevent exposure to hydrogen sulfide, it is critical to audit processes and facilities for potential sources of leaks. This includes reviewing gas detectors in place to make sure they provide adequate detection coverage. Facility expansions, upgrades, and retrofits have the potential to introduce new hazards or reduce the effectiveness of gas monitoring equipment already in place.
S4000TH H2S Gas Detector
The General Monitors S4000TH is a hydrogen sulfide gas detector suitable for use in SIL 3 systems and approved by CSA and FM. Additionally, the detector is compliant with the ATEX directive and has the CE Marking. Gas concentrations are displayed on a three-digit LED enclosed in an explosion-proof housing. The S4000TH is also available with an optional relay configuration that is appropriate for SIL 2 processes.
The S4000TH is easy to maintain. Because of the detector’s multiple communication methods, a user can perform gas checks or single point calibrations through a magnet menu, HART, or Modbus. No special tools or area declassification is required. If, upon performing a gas check, the unit does not read ±10% of the concentration of the calibration gas, the user can re-apply the magnet (or send a new HART or Modbus command) to calibrate it. This reduces the amount of H2S calibration gas and time required to perform routine maintenance. The S4000TH also stores the maintenance event with date and time stamp for improved record keeping.
But beyond ease of calibration and event logging, the S4000TH is equipped with a precise and reliable metal oxide semiconductor (MOS) sensor. Laboratory tests have shown these sensors to be highly selective; unaffected by ammonia, hydrogen, alcohols, and other gases commonly present in plant environments. The detector monitors H2S gas to the parts per million (ppm) and provides status indication and alarm outputs. Sensors are available in 0-20 ppm, 0-50 ppm or 0-100 ppm to support a wide range of applications. The MOS sensors also comply with ISA 92.0.01 Part I – 1998. In addition, the S4000TH can be equipped with relay contacts that indicate an alarm or fault condition, dual redundant Modbus, or HART communication.
Download the S4000TH data sheet.
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