Gas Detection
Gas detection works in tandem with other fire detection systems, like smoke, heat, and flame detectors.
- Wherever highly combustible gases are present
- Where an immediate response to gas is required
- Where a substantial capital investment needs to be safeguarded are the typical applications for gas detectors.
List few examples of Gas installation unit
- Mines, refineries, ship hulls
- Sewage treatment facilities
- Manufacturing facilities,
- Pipeline pumping stations,
- Gas transport loading terminals
- Offshore drilling and production platforms
How to connect a gas detector?
Three alternative connections can be made between gas detectors in order to deliver various levels of information.
1. Stand Alone – The detector has built-in relays that emit alarm and fault signals. The detector activates warning devices when it detects the predetermined level of gas. The unit may feature LED indicators, but a stand-alone setup has the drawback that there is no central remote indication in the event of an emergency or failure.
2. Control Panel – The detector is attached to a control panel specifically for gas detectors. The purpose of this panel is to offer centralized monitoring of numerous detectors, and it might include single cards with analogue and digital displays. The power supply to the detectors is checked, and warning devices can be actuated from the panel as well.
3. Monitoring System: A 4-20 mA output from the detector links to a site monitoring system. Multiple alarm and fault conditions are provided via the output. The benefit of this system is that gas detectors can be integrated into a system that is monitoring other site operations, including air conditioning.
What are the types of Gas detectors?
Currently, there are three different types of gas detectors.
- IR Gas Detectors
- Electrochemical Gas Detector
- Catalytic Gas Detector.
IR gas detectors
- Based on the energy that hydrocarbons absorb, infrared gas detection is used to find flammable amounts of hydrogen gases and vapor. Point and open path detection are two different forms. The IR beam is delivered over a long distance (up to 150m), it is a two-part detector (transmitter and receiver), and they provide a reading in LEL meters.
- In storage tank the sample is around by a point-type detector that is placed as close to the risk as possible. Between a source and detector, an IR energy beam is produced in the detector, and any hydrocarbon-induced attenuation in the short beam is electronically processed to produce a reading in LEL.
- To detect an evaporating gas cloud, open path detectors can be employed as an electronic fence around a facility’s perimeter.
Electrochemical gas detectors
Electrochemical sensors are able to detect concentrations in the parts per million range and are meant to be very selective. Oxygen, hydrogen sulphide, carbon monoxide, nitrogen dioxide, and sulphur dioxide are among the gases that have been found. Multiple electrodes submerged in an electrolyte are used in the sensors. An electrochemical reaction that takes place as gas diffuses into the sensor results in a current that is proportional to the gas concentration.
Catalytic Gas Detectors
What function does a catalytic gas detector?
Up to 100% of the LEL, flammable gas concentrations can be measured using a catalytic bead combustible sensor. When a monitor is used to measure the same gas that it was calibrated with, the readings will be the most accurate.
Principle of Catalytic Gas Detector
A Wheatstone bridge circuit with two computer-matched components is used in catalytic sensor technology. As combustible gases and vaporsoxidize on the active catalytic element, they are detected. Up to its lower explosive limit (LEL), this reaction generates a differential voltage that is proportionate to the gas concentration present.
Working of Catalytic Gas Sensor
- The workings of catalytic sensors are the oxidation of flammable gases, which occurs when combustible gases come into contact with the catalyst surface.
- The reaction generates heat, which modifies the wire’s resistance. A very small coil of platinum wire is placed inside a ceramic pellet to create a catalytic palletized resistor, also known as a “Pellistor”.
- A layer of a high surface area noble metal is present on the surface of the pellet, and it functions as a catalyst to encourage the exothermic oxidation of combustible gases when heated.
- During operation, a current is sent through the underlying coil to heat the catalyst layer.
- The hot catalyst enables oxidation to take place in the presence of flammable gas in a chemical reaction comparable to combustion. Similar to combustion, the reaction generates heat, which raises the temperature of the catalyst as well as that of the coil and pellet beneath it. This increase in temperature causes a change in electrical resistance, which is what the sensor’s signal is.
- Pellistor sensors are always produced in pairs, with the active catalyzed element paired with a non-catalyzed element that has been treated to prevent any gas from oxidizing on its surface.
- In order to exclude the impacts of environmental conditions other than the presence of a flammable gas, this “compensator” element is utilized as a reference resistance to which the sensor’s signal is compared.
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- The active sensor and the reference bead are both affected by environmental factors like temperature, humidity, and pressure variation, therefore the Wheatstone bridge won’t become unbalanced.
- This feature enables the Pellistor to offer a careful read-out even in challenging environmental circumstances.
How does a catalytic combustion sensor work?
- Catalyst sensors consists of two primary components: a detector that is made up of a catalytic material that is sensitive to flammable gases, and a compensator component that is made up of an inert material. Combustible gases only burn the presence of oxygen on gas detector, generates a rise in temperature and a correspondingly electrical resistance rises.
Characteristics Features of Catalytic Detector
A professional catalytic sensor has a number of advantages in addition to its capacity to account for changes in the environment:
- Reproducibility is the ability to obtain the same value, related to the same concentration and environmental conditions, on more sensors of the same type and manufacturer.
- Linearity is the linear relationship between zero and the span gas value.
- Repeatability is the percent error between the reading generated by a second application of calibration gas and the first benchmark value, compared to the range.
Catalytic Gas Sensor Application
- Within the Lower Explosive Limit (LEL), the catalytic sensor is suitable for the detection of a variety of combustible gases. mV
- The gas being detected determines the response time; the greater the gas weight or molecule dimension, the longer the response time.
- With T50 2 sec and T90 response to methane detection takes between 5 and 10 seconds; a minor delay happens if the sensor is shielded by a sintered filter.
Catalytic Sensor Restriction
Certain contaminants may affect how well a catalytic sensor performs. Inhibitors and toxins are two categories into which these can be separated.
Inhibitors
- Inhibitors impair the sensor’s sensitivity momentarily.
- After a brief exposure to fresh air, sensitivity may return in full or in part. \
- H2S, chlorine, chlorinated hydrocarbons, and halogen compounds are the most prevalent inhibitors.
Poisons
- Poisoning substances permanently reduce the sensor’s sensitivity, completely damaging it.
- Tetraethyl lead and silicon compounds are two of the most prevalent toxins.
- The most frequent reason for issues with gas detection is the existence of inhibitors or toxins, thus caution must be taken to prevent contamination.
Advantages of catalytic gas detector
- Reacts to nearly all flammable and combustible gases include hydrogen, hydrocarbon and non-hydrocarbon gases
- Broad gas detection range of the catalytic bead.
Disadvantages of catalytic gas detector
- Regular calibration is necessary for efficient protection Over time, sensors do “wear out,” and they are unable to detect non-combustible gases. Sensors may be contaminated
Frequently Asked Questions:
What distinguishes catalytic gas detectors from infrared gas detectors?
Catalytic sensors provide dependable protection, although they are more vulnerable to some types of pollution than infrared detectors. In contrast, infrared detectors lack the robustness or capacity to function in a multi-gas environment, which makes them a less desirable option for some tasks.
What major four gases are there in a gas detector?
By evaluating the four major gases you’re testing for—oxygen (O2), carbon monoxide (CO), hydrogen sulphide (H2S), and methane (CH4)—a 4 gas monitor will help you protect your employees in any setting.
What is a catalytic sensor’s operating range?
Lower Explosive Limit (LEL) detection range is 0 to 100%. The entire sensor is made up of an interface module and a stainless-steel sensor head assembly that are both housed in a flame-resistant instrument enclosure.
What is the limitation of a combustion gas detector of catalytic combustion type?
The fact that these sensors need a certain minimum concentration of oxygen in order to identify whether or not a given gas sample is combustible is one of the drawbacks of catalytic technology.
