One, overview

Expansion joint is a flexible structure set on the shell of a pipe or container to compensate for additional stress caused by temperature difference or mechanical vibration. There are many types of expansion joints, commonly used metal bend expansion joints, metal bellows expansion joints, metal sleeve expansion joints, rubber duct expansion joints, fiber fabric expansion joints.

As far as the sulphuric acid device is concerned, the expansion joint mainly adopts U-shaped corrugated expansion joint. The corrugated expansion joint of the sulphuric acid gun uses the effective expansion and deformation of the bellows to absorb the dimensional changes caused by thermal expansion and cold contraction of the sulphuric acid gun pipeline, so as to avoid serious deformation or damage of the sulphuric acid gun due to thermal elongation or temperature stress.

Two, the reason for the explosion of the expansion joint

The U-shaped corrugated expansion joint used in the sulfer gun is the weakest position of the gun body. The pressure of the thermal insulation steam used in the sulfer gun in the production of sulfuric acid is 0.3MPa ~ 0.4MPa. Taking the sulfer gun produced by our company as an example, the thickness of the corrugated expansion joint is 0.8mm and the designed pressure is 1.6MPa. The actual water slow pressure test has a maximum pressure of 3.5MPa.

According to the relevant investigation, the failure causes of corrugated expansion joints on the sulfonate gun are mainly divided into three categories: bump, fatigue, overpressure explosion.

Bump will lead to the loss of deformation ability of the U-shaped ripple above the corrugated expansion joint, resulting in loss of compensation ability. The corrugated expansion joint itself is made of metal and the working temperature is high, there is metal fatigue aging phenomenon, resulting in the failure of the corrugated expansion joint. The burst of the corrugated expansion joint of the sulfogun is mainly caused by the overpressure of the sulfogun steam jacket. For example, the steam trap is closed so that the condensate of the thermal insulation steam enters the sulfogun, and the steam outlet stop valve is closed at the same time. Then the condensate is heated and expanded in the sulfogun (the volume of water transformed into steam expands by 500~600 times), resulting in a sharp rise in the pressure of the steam jacket layer of the sulfogun. The instantaneous pressure exceeding the corrugated expansion joint causes the corrugated expansion joint to burst.

The condensed water in the steam jacket of the sulfonic gun can be heated into steam and the pressure after expansion can be roughly calculated using the ideal gas equation of state:

P is the pressure at which water becomes steam when heated (Pa)

V is the gas volume (m³) : According to our standard sulfonate gun as an example, the volume of steam jacket is about 28L, that is, 0.028m3

n is the amount of substance (mol) of the gas: calculated according to 200g condensate water, that is, 11.11mol

R is the molar gas constant (also known as the universal gas constant) (J/(mol.K)) : the constant is 8.314J/(mol· K)

T is the temperature (K) : calculated according to the temperature of 900℃ in the sulfur burning furnace, that is, 1173.15K

Through calculation, it can be concluded that the pressure of 200g condensed water after thermal expansion in the sulfonate gun is about 3.87MPa, which is far beyond the pressure of the corrugated expansion joint of the sulfonate gun, which will lead to its explosion and cause accidents.

Three solutions

When the gun is installed on the sulfur burner

1. The steam trap stop valve before the inlet of the thermal insulation steam should be opened first, and the condensate in the thermal insulation steam should be drained clean to ensure that the thermal insulation steam entering the sulfonate gun does not contain condensate water;

2. Confirm that the steam outlet of the sulfogun insulation steam is in the empty state, slowly open the secondary stop valve of the steam inlet of the sulfogun insulation steam, and use the steam to cool the sulfogun to the range of 133 ~ 160℃;

3. After the device runs normally, the thermal insulation steam of the sulfonator gun can be turned off to ensure that no condensate is generated in the steam pipeline, reduce the consumption of thermal insulation steam and prevent the leakage of thermal insulation steam into the sulfur burning furnace;

4. At the same time, keep the steam outlet of the sulfonate gun empty the gutter to check whether there is liquid sulfur leakage of the sulfonate gun.

The installation and piping diagram of the sulfonate gun is shown in the following figure: