Online analytical instruments have been widely used in the chemical industry, providing important means and basis for chemical production process control, product quality improvement, and operation guidance. The online analysis instrument continuously and automatically analyzes the component content and individual component content of various mixed gas samples at the production site, making the process control more timely and accurate. However, in the actual production process, many online analytical instruments cannot be put into operation normally, reliably and continuously, and cannot really play their roles. The main reason is that the process site has insufficient understanding of the operating conditions of online analytical instruments, and sample pretreatment cannot make the measurement sample. The gas meets the requirements of the analyzer, which restricts the use and development of online analyzers.

 

1Online analyzer pretreatment system

 

1.1 Basic tasks and functions of sample pretreatment

 

Online analyzers usually require clean, non-corrosive samples that do not contain interfering components. Under normal circumstances, the samples must be within the limited temperature, pressure, and flow range. The basic tasks and functions of sample processing are summarized as follows: Flow adjustment , Including fast flow path and analysis loop: pressure adjustment, including pressure reduction, suction and stabilization; temperature adjustment, including cooling and heat preservation: dust removal, dehumidification and gas-liquid separation, removal of harmful substances, including those harmful to the analyzer Components and disturbing components that affect the measurement.

 

1.2 The sample pretreatment system is divided into pretreatment and pretreatment systems

 

The pre-processing unit performs preliminary processing on the sample taken out to make the sample suitable for transmission, shorten the transmission lag of the sample, and reduce the burden on the processing unit, such as decompression, cooling, dust removal, degassing and other pretreatment units to further process the sample And adjustment, such as temperature, pressure, flow adjustment, filtration, dehumidification, removal of harmful substances, etc., safe pressure relief, flow restriction and flow switching, etc.

 

1.3 The purpose of the sample pretreatment system is to provide online analytical instruments with continuously updated, clean, and representative sample gases with temperature, pressure and flow suitable for the working conditions of online analytical instruments. In coal chemical plants, most process conditions None of them can meet the requirements of the working conditions of online analytical instruments, and a sample that meets the operating conditions of the instrument is very important for online analysis.

 

  1. System structure

This system is composed of alcohol washing tank, water washing tank, neutralization tank, gas-liquid separation filter, gas source processor, vacuum generator, sampling/vent flow meter, pressure regulating valve, analysis instrument, etc. The calibration system is composed, and the parts other than the sampling probe are installed inside a standard case. The pretreatment components are all to ensure the long-term reliable operation of the gas analysis instrument.

 

2.1, system working principle

The sample gas to be tested is taken out through the sampling pipeline, the sample gas at the sampling point is physically/chemically dissolved and neutralized, dust removed, constant temperature, water removed, dried, and constant current is sent to the analysis instrument, and the field test data is sent to the 4-20mA PLC/DCS can also be sent to the IoT cloud platform through the GPRS network.

2.2. Pretreatment system

 

①. Alcohol washing tank: It is used for gas scrubbing and added to ethanol solution with a concentration greater than 90% to dilute the VOC organic volatile gas in the dissolved sample gas. The liquid surface needs to be more than 2cm over the sampling nozzle.

 

②. Neutralization tank: For gas scrubbing, add 50% sodium hydroxide solution to neutralize the acid gas in the sample gas. The liquid surface needs to be 2cm over the inlet of the sample gas.

 

③. Water washing tank: used for gas scrubbing, adding drinking water solution, diluting solvent components that can dissolve in water such as ethanol in the sample gas, and the liquid surface needs to be 2cm over the injection nozzle.

 

④. Gas-liquid separation filter: The filter element is used to filter trace dust and tar impurities, and can play a role in removing liquid water.

 

⑤. Vacuum generator: The function is to continuously extract slightly positive or negative pressure sample gas to the pretreatment system; it needs a compressed gas source of 0.2-0.5MPa to drive work; the compressed gas source needs to be dry and oil-free. IN air inlet, OUT air outlet.

 

⑥. Pneumatic condenser: instantaneously condense the sample gas to -4-30 degrees Celsius, convert the gaseous state to liquid and discharge it.

 

⑦. Air source processor: internally equipped with color-changing silica gel for drying sample gas, or built-in activated carbon to adsorb VOC organic gas. When the color-changing silica gel absorbs water and turns red, it needs to be replaced in time.

 

⑧. Sampling flow meter: Control the sampling flow to 0.5L/min, turn it down counterclockwise and turn it up clockwise.

 

⑨. Pneumatic diaphragm pump: It needs a compressed air source of 0.2-0.5MPa to drive work; the compressed air source needs to be dry and oil-free. IN air inlet, OUT air outlet.

 

⑩. Pressure regulating valve: used to regulate the air source pressure of the vacuum generator/vortex condenser/pneumatic pump.

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