The Working Principle Of The Water Seal Tank

In batch-type thermal cracking oil refining equipment, the working principle of the water seal tank is based on three core mechanisms: water layer sealing, gas-liquid mass transfer, and pressure balance, which can be specifically divided into three key stages:

Sealing and Backfire Blocking Mechanism

A fixed volume of clean water is pre-filled in the water seal tank, and the gas outlet of the non-condensable gas transmission pipeline must be submerged to a certain depth below the water surface. Under normal operating conditions, the non-condensable gas breaks through the water layer by virtue of its own pressure, escapes above the water surface, and enters the subsequent combustion or treatment system. If backfire occurs in the downstream combustion system, the flame will spread to the inlet of the water seal tank, but the water layer will form a physical barrier, completely blocking the path of flame flashback. This prevents the flame from entering the upstream cracking reactor or non-condensable gas storage tank, and fundamentally avoids the ignition and explosion of combustible gases.

Gas-liquid Separation and Impurity Purification Mechanism

The non-condensable gas generated by cracking carries impurities such as light oil mist, water vapor, and solid dust. When the gas passes through the water layer in the form of bubbles, the oil mist comes into contact with water and dissolves in it; the solid dust is adsorbed and settled by water; and the high-temperature water vapor condenses into liquid water upon cooling. After washing and separation by the water layer, impurities in the non-condensable gas are effectively removed. The purified gas enters the subsequent pipelines, which can prevent blockage or corrosion of pipelines, valves, and burners.

Pressure Regulation and Overpressure Relief Mechanism

The pressure threshold of the water seal tank is determined by the height of the water layer: the higher the liquid level, the greater the water pressure that the gas needs to overcome, and the higher the upper limit of the system’s safe pressure. When the pressure inside the cracking system or non-condensable gas pipeline rises abnormally, the high-pressure gas will push the water layer open, forcing the excess gas to discharge directly through the overflow port or vent port of the water seal tank into the flare system or a safe area, realizing passive overpressure relief and preventing pipeline or equipment rupture due to overpressure. Meanwhile, the stable water layer can also buffer pressure fluctuations in the pipeline, ensuring the stability of non-condensable gas transmission.