First, let's popularize some common sense. Gas detectors have a range of applications, which is usually mentioned in technical documents. In terms of gas temperature, flammable and oxygen do not require pre-treatment because they are used in many places and specific equipment has emerged. So, what are the prerequisites for pre-treatment of gas detectors? Let's take a look together with the editor next!

High temperature combustible and zirconia are gas detectors that do not require pre-treatment. High temperature combustible is generally used to measure combustible gases in places between 400-600 degrees Celsius, while zirconia is an insert type suitable for measuring oxygen in places above 100 degrees Celsius and below 800 degrees Celsius. (Insertion type)

There are also some situations that do not require pre-treatment. Firstly, for strong pressure, pre-treatment can be omitted and only a pressure reducing valve can be installed. For negative pressure, pre-treatment is not necessary and only a pump needs to be installed.

Preprocessing is mainly applied to three situations:

1. Need to cool down (the above two gases are not needed);

2. Need to remove water (even in the absence of small water droplets due to high humidity);

3. Dust removal.

Overall, if the temperature is above 70 degrees Celsius and there are small water droplets on the surface, pre-treatment is required. Electronic condensers are used for cooling, compressors are used for water removal, filters are used for dust removal, and sampling pumps cannot be used under vacuum. Everyone should pay attention to this.

Also, if there is oil, pre-treatment cannot be used. This does not mean oil and gas, but liquid oil. Liquid oil can hinder the operation of the pre-treatment system. In fact, this type of exhaust gas online monitoring system, as well as CEMS that people may have less exposure to, can be classified as a type of pre-treatment in principle.

Due to the fact that most of these products are customized, the price is relatively high. However, because their shells are mostly corrosion-resistant and have excellent performance, their service life is more than 1.5 times that of ordinary detectors, gradually becoming the first choice for many large enterprises!

　　Pre treated gas analyzerIt is a solution for gas pretreatment and online monitoring in harsh environments such as high temperature, high humidity, high dust, and oil-water mixing in industrial production processes. After gas pretreatment, clean gas that meets the requirements of gas analyzers can ensure the accuracy of gas detection and analysis to a certain extent, effectively extend the service life of gas detection core components, and improve the reliability and stability of detection. The pre-treatment gas analyzer is equipped with a heat dissipation and exhaust filtration system, ensuring a clean and stable processing environment inside the box. The analysis of gas concentration in harsh industrial sites is of great significance.

　　Application field

Multi component pre-treatment gas analyzers are widely used in industries such as environmental protection, energy, chemical, metallurgical, and power. For example, it can be used to monitor air pollution, indoor air quality, industrial exhaust emissions, etc; It can also be used to monitor gas leaks, coal mine safety, etc.

Gas pretreatment system is a solution for gas pretreatment and online detection in harsh environments such as high temperature, high humidity, high dust, and oil-water mixture in industrial production processes. After pre-treatment, the target gas can be transformed into a clean gas that meets the requirements of the gas analyzer. This can ensure the accuracy of gas detection and analysis to a certain extent, and effectively extend the service life of gas sensors and improve their reliability.

The gas pretreatment system consists of the following parts:

Efficient condensing device: This system uses a semiconductor electronic condenser to ensure efficient condensation and water removal of the tested gas.

Three stage filtration device: oil removal, dust removal, and drying.

Automatic drainage device: using a long-life peristaltic pump to ensure timely drainage of condensed water.

Temperature monitoring and control: Adopting inlet temperature monitoring and control devices, sensor temperature and humidity monitoring devices to ensure that the condenser is not affected by high temperatures.

Gas sampling device: Equipped with a powerful vacuum pump, it has a long lifespan and high load capacity.

Gas detection device: supports 1-4 gas sensors and can monitor simultaneously.

Data transmission: Remote data transmission system (4-20mA, RS485, TCP/IP network port transmission, etc.)

SMS alarm device: SMS alarm can be triggered through the mobile phone module.

What is a pressure reducing gas sampling probe?

The pressure reducing gas sampling probe is a type of probe that combines a pressure reducing valve and a sampling tube to reduce the pressure of the sample before removing it. It is called a GPR (Genie Probe Regulator) probe in foreign countries, which can be translated as a Genie probe pressure regulator or Genie pressure reducing adjustment probe. It was developed by the American company A⁺The company develops and produces. This probe is commonly used for sampling natural gas pipelines and can operate at a pressure of 14MPaG (2000psiG). Its advantage is that it can prevent natural gas condensate from entering the analyzer, and can also be used for sampling other easily liquefied gases or medium to high pressure gas samples. The lower end of the probe is equipped with a thermal fin, which is used to compensate for the thermal mass of the airflow by absorbing heat through the fin when the sample expands under reduced pressure and humidity decreases.

What are the basic requirements for sample transfer in gas analysis systems?

(1) The transmission lag time should not exceed 60 seconds, which requires the distance between the gas analyzer and the sampling point to be as short as possible, the distance between the transmission system to be as small as possible, and the sample flow rate to be as fast as possible (preferably between 1.5-3.5 m/s, so a high-power vacuum pump is selected as the boosting device).

(2) If there is a time lag of 60 seconds at the flow rate allowed by the gas analyzer, a fast loop system should be used (such as a vacuum pump with a pumping volume of 6L/min, but the analyzer only needs 500ml/min, and all excess sample gas should be discharged).

(3) It is best for the gas transmission pipeline to reach the gas analyzer straight with only a few corners.

(4) There are no dead branches or dead volumes.

(5) For gas samples containing condensate, the transmission pipeline should maintain a certain slope downward, and the low point should be close to the gas analyzer and equipped with a condensate collection tank. The slope gradient is generally 1:12, and for viscous condensate, it can be increased to 1:5.

(6) Prevent phase transition, that is, during the transmission process, the gas sample remains in a gaseous state and the liquid sample remains in a liquid state.

(7) The sample pipeline should avoid passing through areas with humidity changes, which can cause uncontrolled changes in sample conditions.

(8) The sample transmission system must not have any leaks to avoid sample leakage or environmental air intrusion.

What is the function of the sample gas processing system? What is its importance?

The function of the sample processing system is to ensure that the gas analyzer obtains representative process samples in the shortest possible lag time, and the state of the samples (humidity, pressure, flow rate, and cleanliness) is suitable for the operating conditions required by the gas analyzer.

The effectiveness of online gas analyzers often depends not on the gas analyzer itself, but on the completeness and reliability of the sample system. Because, no matter how complex and precise the gas analyzer is, its analysis accuracy is also limited by the representativeness, real-time performance, and physical state of the sample. In fact, there are often more problems encountered in the use of sample systems than gas analyzers, and the maintenance of sample systems often exceeds that of gas analyzers themselves. So, it is important to value the role of the sample system and at least consider it in the same position as the analyzer.

What are the basic requirements for gas sample systems?

(1) Make the sample obtained by the gas analyzer consistent with the composition and content of the material in the process pipeline or equipment.

(2) The consumption of process samples is minimized.

(3) Easy to operate and maintain.

(4) Can work reliably for a long time.

(5) The system composition should be as simple as possible.

(6) Adopting a fast loop to reduce sample transfer latency.

How to choose the location of the sampling point?

When selecting the sampling point position for a gas analyzer on a process pipeline, the following principles should be followed, and the optimal position may be a trade-off between some of the following points:

(1). Sampling points should only be located at sensitive points that reflect changes in the properties and composition of the process fluid;

(2). The sampling point should be second only to the most suitable position for process control to avoid unnecessary process lag;

(3). The sampling point should be second only to the location where the available process pressure difference forms a rapid circulation loop;

(4). The sampling point should be selected at a location where the sample temperature, pressure, cleanliness, dryness, and other conditions are as close as possible to the requirements of the gas analyzer, in order to minimize the number of sample processing components (the more components there are, the more hidden dangers there are);

(5). The sampling point should be easily accessible from escalators or fixed platforms;

(6). The online analyzer and laboratory analysis sampling points should be set separately.

It is generally believed that in most gas and liquid pipelines, sampling from turbulent locations that produce good mixing can ensure that the sample is truly representative. Because it is not easy to achieve mixing of gas or fluid mixtures unless turbulence exists, the sampling point can be selected after one or more 90 degree elbows, immediately downstream of the last elbow, or at a relatively calm position downstream of the throttling element (not close to the throttling element).

Try to avoid the following situations as much as possible.

(1) Do not take samples downstream of a relatively long and straight pipeline. Because the fluid flow at this location is often laminar, the concentration gradient on the cross-section of the pipeline can lead to non representativeness of the sample composition.

(2) Avoid sampling in locations where pollution may exist or in dead volumes where gases, vapors, liquid hydrocarbons, water, dust, and dirt may accumulate.

What probe should be used for sampling clean samples, dusty gas samples, and dirty liquid samples?

For clean samples or samples with low dust content (<10mg/m)³）Gas samples are collected using a straight through (open) sampling probe with a 45 º angle incision facing away from the fluid flow direction.

High dust content (>10mg/m)³）The gas sample can be sampled using a filtering probe. The probe with a filter installed at the head of the probe (inside the process pipeline) is called a built-in filter probe, and the probe with a filter installed at the tail of the probe (outside the process pipeline) is called an external filter probe.

For the sampling of complex condition samples such as ethylene cracking gas, catalytic cracking regeneration flue gas, sulfur recovery tail gas, coal or heavy oil vaporization gas, urea acid gas, etc., a specially designed dedicated sampling device should be used.

How should the length of the sampling probe be determined?

The length of the probe mainly depends on the insertion length. In order to ensure the representativeness of the extracted sample, it is recommended that the insertion length be at least equal to 1/3 of the inner diameter of the pipeline.

What direction should the gas sampling probe be inserted into the process pipeline from?

The insertion orientation of gas sampling probes should be considered as follows:

1. For gas sampling in a horizontal pipeline, the probe should be inserted from the top of the pipeline to avoid possible condensation or droplets. The probe should be inserted from the side wall of the pipeline to avoid possible vapor in the upper part of the pipeline, as well as possible residue and sediment at the bottom of the pipeline.

2. Insert the vertical pipeline from the side wall of the pipeline.

What types and specifications of Tube tubes are used in online gas analysis instruments and sample processing systems?

The commonly used Tube tubes are classified by material, mainly including 316 stainless steel and 304 stainless steel; According to the forming process, there are two types: seamless steel pipes (hot-rolled and then cold drawn) and welded steel pipes (welded with strip steel); There are two measurement units used according to their outer diameter and wall thickness dimensions: inch tube and meter tube.

What types of pipe fittings are used in online gas analysis instruments and sample processing systems?

Answer: There are many types of pipe joints, but they can be classified into the following categories.

1. Union fittings are used for connecting pipes between pipes, or joints that use card sleeves on both sides. There are mainly the following types: straight through Union fittings; Three way intermediate connector (UnionTee); Four way intermediate connector (UnionCross); Union Elbow (with two types of 90 º and 45 º bends); Bulkhead Union.

2. Reducing Union is used for connecting pipes of different diameters, commonly known as large and small heads, and is also an intermediate joint.

3. Terminal connectors are used to connect Tube tubes with analyzers, sample processing components (filters, pressure reducing valves, flow meters, sample pumps, etc.). This type of joint, which is connected to the Tube tube with a sleeve on one side and to the analyzer and sample processing components with threads on the other side, is the connector at the end of the Tube tube, hence it is called a terminal joint. There are mainly the following types: direct terminal connectors; Three way terminal connector (ConnectorTee); ConnectorElbow (with two types of 90 º and 45 º bends); Bulkhead Connector.

Gauge Connector is used for connecting Tube pipes and pressure gauges, and is also a type of terminal connector. There are mainly two types: straight through (GaugeConnector) and three-way (GaugeConnectorTee).

5 Other components such as adapters, flug plugs, caps, etc. will not be further elaborated.

What is sampling pipeline heat tracing? What is insulation?

Heat tracing uses steam and electric heat tracing tubes to heat the sample pipeline, supplementing the heat lost during the transportation process to maintain the sample humidity within a certain range.

Thermal insulation is a covering measure taken on the outer surface of the sample pipeline to reduce heat dissipation to the surrounding environment or heat absorption from the surrounding environment during transportation. Or, in other words, isolation measures taken to ensure that the sample is not affected by the ambient temperature during transportation.

Why do sample transfer pipelines need to be heat traced or insulated? Which samples require heat tracing or insulation transmission?

In petrochemical plants, sample transfer pipelines often require heat tracing or insulation to ensure that the phase and composition of the sample do not change due to temperature changes. A significant source of temperature variation during sample transportation is weather changes. China is located in a continental monsoon zone, and the temperature difference between winter and summer often exceeds 60 ℃. In addition, the heating effect of direct solar radiation must also be considered. Under summer sunlight exposure, the surface temperature of the sample pipeline can sometimes reach 80-90 ℃. Therefore, in the design of sample transmission, the influence of environmental temperature changes on the coarseness and composition of the sample must be considered.

The gas sample contains components that are prone to condensation and should be accompanied by heat insulation above its dew point; The liquid sample contains components that are prone to gasification, and should be insulated and kept below its evaporation temperature or maintained at a pressure above its vapor pressure. Microanalysis samples (especially trace amounts of water and oxygen) must be transported with heat because the adsorption effect of the tube wall increases with decreasing temperature, while the desorption effect shows the opposite trend. Samples that are prone to condensation and crystallization must also be accompanied by heat transfer. In short, the insulation method should be selected reasonably and the insulation temperature should be determined based on the sample conditions and composition, as well as the changes in environmental temperature.

What are the advantages and disadvantages of steam tracing?

The advantages of using low-pressure steam tracing are high temperature and large heat, which can quickly heat the sample and keep it at a high temperature. Its disadvantages are as follows:

1 . The effective heat tracing length of the steam tracing system is greatly limited due to the small diameter of the steam pipe, the inability of the air pressure to be too high, and the variation in the height of the riser. As a result, when the sample pipeline is long or heavy load heat tracing is required, segmented heat tracing is necessary. According to foreign data, the maximum effective tracing length for steam tracing is 100ft (30.48m). Therefore, for a 60m long sample pipeline, it is generally necessary to divide it into two tracing sections.

2 . The fluctuation of steam pressure can cause significant temperature changes, and insufficient gas supply or even short-term interruptions can occur, making it difficult to achieve the requirements of balanced and stable sample pipeline heat tracing temperature.

3 . When steam tracing is used for the sample pipeline, it is very difficult or uncontrollable to control the tracing temperature (a temperature control valve can be used for the sample processing box).

Compared to steam tracing, what are the advantages of electric tracing?

At present, most domestic petrochemical enterprises use steam tracing method, mainly because it can utilize the existing steam boilers in the plant, but its tracing efficiency and future maintenance and water pump operation are far less economical than using electric tracing. In addition, the materials, insulation installation, and future maintenance costs of the steam supply and return pipelines, as well as the cost of steam water, are also considerable. Compared with steam tracing, electric tracing also has the following advantages.

Electric tracing is a relatively simple tracing system, unlike steam tracing which requires complex steam supply and return pipelines. The required power supply and distribution facilities can be shared with other electrical circuits.

The heat loss range and operation and maintenance costs of electric tracing are limited to the tracing pipeline.

Electric tracing is an easily controllable tracing system, and its temperature control can be very precise, which cannot be achieved by steam tracing.

4. No noise or pollution, steam tracing has the phenomenon of "running, emitting, dripping, and leaking", while electric tracing does not.

The service life of 5 electric heat tracing belts can reach 25 years or even longer, which is difficult to achieve with steam heat tracing.

Easy to install, use, and maintain.

Many developed countries have widely adopted electric heat tracing technology in the industrial field. Currently, many newly built large-scale petrochemical projects in China have adopted electric heat tracing for their instrument systems. However, it should be noted that the temperature range of electric tracing is usually below 200 ℃, while the temperature range of steam tracing can reach 450 ℃. Some samples still require steam tracing for vaporization and transportation.

What are the basic tasks and functions of sample processing?

Answer: An analyzer usually requires clean, non corrosive samples that do not contain interfering components. Under normal circumstances, the samples must be within a limited temperature, pressure, and flow range. The basic tasks and functions of sample processing can be summarized as follows:

Flow regulation, including fast loop and analytical loop;

Pressure regulation, including pressure reduction, suction, and stabilization;

Temperature regulation, including cooling and insulation;

• Dust removal;

• Dehumidification and gas-liquid separation;

Remove harmful substances, including components that are harmful to gas analyzers and interfering components that affect analysis.

What are the commonly used flow control components in sample processing systems?

Answer: (1) Ball valves have a spherical valve core, which is used to cut off or connect the sample flow path. Two way ball valves (2-WayBall Valves) and three-way ball valves (3-WayBall Valves) are widely used in sample processing systems. According to the driving mode, two-way and three-way ball valves can be divided into manual, pneumatic, and electric types. In addition, sometimes four-way, five way, six way, and seven way ball valves are also used in small quantities.

(2) Plug Balves have a cylindrical valve core that functions similarly to a two-way ball valve.

(3) CheckValales, also known as check valves, only allow one-way flow of the sample and cannot flow in the opposite direction.

(4) Needle Valves have a conical valve core, which is used to fine tune sample flow and pressure.

(5) Steady flow valves are used to stabilize sample flow and pressure.

(6) The limiting valve and limiting orifice plate limit the sample flow rate to a certain allowable value, providing safety protection.

(7) Float flowmeter, also known as rotor flowmeter, is used to indicate sample flow rate. There are two types of conical tube materials: glass and metal, and several float materials including stainless steel, copper, aluminum, plastic, etc. Float flow meters with needle valves are commonly used in sample systems, which can indicate and adjust flow rates. Sometimes a float flow rate with a low flow rate alarm is also used to issue an alarm signal when the sample flow rate is below the specified value, in order to prevent the analyzer from issuing incorrect flow signals.

Gas Multi channel Sampling Flow Switching System

In multi channel analysis, a multi channel switching system is required. Compared to several single channel analyzers, a multi channel analyzer can save a lot of money. But multi flow analysis systems have a higher failure rate and maintenance workload. When the analyzer malfunctions and shuts down, the analysis of all flow paths is interrupted and information is lost. There may be gas leakage between samples, and the analysis interval period is relatively long.

Common faults in flow path switching systems include valve leakage, unclean sample replacement, and mixing between flow path samples.

The flow switching system often adopts the following two methods

1. Cut off and release the system

A two-way double blocking system using two three-way valves is constructed as shown in the figure.

N in the picture_OThree flow paths have been selected. N_O1 and N_OThe samples in the two flow paths are blocked by dual valves, and the samples retained in the dead volume between the dual valves or the small amount of samples occasionally leaked into the flare system due to valve leakage are discharged through the bypass pipeline, which will not affect N_OThree flow paths cause pollution.

2. Reverse washing system.

The system for backwashing and washing other flow paths using the selected sample flow path is shown in the diagram for its composition and principle.

N in the picture_OThree flow paths have been selected. N_O1 and N_OThe samples of the two flow paths and the standard airflow path are cut off by the pneumatic two-way valve. N_OAt the same time as flowing towards the analyzer, the sample from channel 3 is also backwashed in the opposite direction_O1 and N_OTwo flow paths and a standard airflow path are used to blow out the samples that are retained before starting the above flow path or the small amount of samples that occasionally leak into the valve, and then discharge them into the flare system through the bypass pipeline, so they will not affect N_OThree flow paths cause pollution.

Principles for emissions after gas sample processing

The sample emission requirements should not pose a danger or cause pollution to the environment.

The emission methods of gas samples include:

1. Discharge the torch or return to the process pipeline.

This is a safe and economical method for handling flammable, toxic, or corrosive gases.

The pressure at the sample return point should be lower than the discharge pressure to maintain a certain discharge pressure difference.

And the return point should not have pressure fluctuations, otherwise it will affect the stability and accuracy of the analysis value.

If there are easily condensable components in the sample, the discharge pipeline should be heat insulated and a condensate valve should be added at an appropriate position to remove the condensate. Prevent blockage of condensate and formation of back pressure.

The centralized discharge of multiple instruments should ensure that the main pipe has sufficient volume, and the diameter of the main pipe should be more than 6 times that of the exhaust pipe of the analyzer. When laying the main pipe horizontally, there should be a slope of 1:100-1:10 to facilitate discharge, and the exhaust pipe should be vertically connected from the upper part of the main pipe to avoid the discharge port being blocked by liquid accumulation or impurities in the main pipe. An exhaust collection tank can also be used instead of the exhaust manifold, with each analyzer's exhaust pipeline connected separately to the tank.

2. Exhaust into the atmosphere.

Direct emissions. Clean, non-toxic, non flammable and harmless to the environment, which can be directly discharged into the atmosphere. Some analyzers that use atmospheric pressure as a reference point, such as infrared and gas chromatography column systems and detector outlets, also require direct discharge into the atmosphere. When discharging, a vertical pipe can be extended from the top of the analysis cabin, and the end of the pipe should be equipped with a protective cover or 180 degrees^◦Bend to prevent rainwater from entering and minimize the impact of wind. If there is condensate, add a low point discharge.

Diluted emissions. Set up a dilution emission system, dilute with compressed air and nitrogen in a dilution tank of sufficient volume to below LEL, and vent through an exhaust chimney (above 6 meters).

For analyzers that use atmospheric pressure as a reference point, attention should be paid to the impact of changes in atmospheric pressure on the display error of the analyzer. Because climate change can cause changes in atmospheric pressure, especially during rainfall, this change cannot be ignored. If necessary, an absolute pressure regulating valve can be installed.

Discharge of liquid samples

The discharge method of liquid samples and the issues to be noted;

1. Return to the process pipeline

Liquid samples are generally returned directly to the process flow, especially when they have product, intermediate product, or raw material value. Liquid samples generally require pumping to provide transmission pressure.

2. On site discharge

If the sample cannot be returned to the process, a small amount of liquid samples that do not contain flammable, toxic, or corrosive components can be discharged into chemical drainage ditches or sewage ditches and sent to the treatment plant for treatment. If they contain the above components, they need to be treated before being discharged. However, it must not be discharged into surface water drainage ditches.

One thing to note is that if the liquid sample contains volatile flammable components or mixed with flammable gas components, they must be removed before discharge.

Sampling and processing system for special samples

Special samples refer to those samples with strict sampling process conditions, complex sample composition, and ineffective sampling processing methods. For example, ethylene cracking gas sampling and sample pretreatment system.

The device consists of four parts: a filtering reflux component, a tubular cooler, a vortex cooling system, and a temperature controller.

The working process is as follows:

1. High temperature, high water content, and high oil dust samples are first filtered to remove a portion of liquid oil droplets.

2. The vortex refrigeration tube generates a refrigerant source with a temperature range of 0-30 ℃. The sample is cooled by heat exchange through a tube type cooler, causing the majority of moisture and heavy hydrocarbons to condense into liquid. It flows down the sample tube, flushes and filters the reflux components, and then returns to the process pipeline.

3. After cooling, the sample is measured using a temperature measuring element. The temperature controller adjusts the compressed air outlet pressure (i.e. adjusts the cold air flow rate) based on the temperature measurement signal to maintain the set cooling temperature, and controls the sample outlet valve to send out the sample that meets the requirements. After simple processing, residual moisture and oil mist are filtered and adsorbed, and then sent to a gas analyzer or chromatograph for measurement.

The use of this type of sampling probe has achieved good results in measuring oxygen content in coke oven gas or gas furnace gas.

Common problems and precautions:

The sampling point for cracking gas is on the outlet pipeline of the rapid cooling device, and the sample contains a large amount of rapid cooling oil. The main problem at this point is oil removal, which does not require the use of a coke removal valve. Therefore, it is important to pay attention to the subsequent separation of oil and gas, strengthen inspection and maintenance, timely detect and take corresponding measures, and avoid the harm caused by oil and gas entering the chromatographic column.

The sample transfer pipeline between the gas analyzer should be made of Ø 10MM stainless steel pipe and equipped with heat tracing and insulation measures.