Zinc oxide adsorption method
Through the history of
Zinc oxide adsorption is used in various natural gas and petrochemical operations in more than 100 industrial plants around the world.
The process described
Gas purification process is by gas through a large surface area of zinc oxide bed, zinc oxide particles into a sphere or extrusion molding.
Nominal particle size between 3/8 and 3/16 (> 6 * sieve less than 4* sieve).
Feed grade zinc sulfate
This method is mainly used as a protection against sulfur, and can reduce the HS in the gas to less than 1 PPM before the gas is in contact with sulfur-sensitive catalysts (such as nickel catalysts used in methanation plants).
Zinc oxide adsorbent is discarded after it is saturated with sulfur, that is, when the critical point of sulfur is greater than the allowable value.
The usual chemical reaction that happens is
ZnO+H2S - > ZnS +H2O
It is more economical to replace one bed with two zinc oxide adsorbent beds.
As shown in figure 2.20 1.
The gas passes through the two beds in series. When the sulfur content of the gas coming out of the first bed reaches the critical point, the adsorbent of the first bed is saturated.
But the second bed can absorb more H2S, and the feedstock gas is transferred to the previously second bed.
The sulfur-saturated adsorbent in the first bed is discarded and replaced with a fresh adsorbent, and the first bed becomes a second bed.
For a given amount of zinc oxide adsorbent, the replacement of the borrow bed may remove more sulfur.
Zinc oxide adsorbent is usually at temperatures of 660 ° F to 840 ° F within the scope of use, 400 when a space velocity.
Low temperature to 70 ° F, can also be used in low temperature when the amount of H2S removal is low.
This method can be used in the range of pressure from atmospheric to 50 (~720psig).
When the raw gas contains about 50ppm H2S or other heat-resistant sulfides, a relatively high airspeed can be used, such as 2000 hours.
When the sulfur content of raw gas is at the level of 1-2 ppmH2S, the air speed can be as high as 2000hz.
Total water soluble zinc sulfate
When operating with a single bed, the critical point of sulfur in the outlet gas is 0.2ppmhzs before, zinc oxide adsorbent should contain 17-18% (weight) of sulfur.
For a two-bed operation, the sulfur capacity can be increased to approximately 25% (by weight) of the adsorption dose after saturation.
When the raw gas containing 1-2 ppmH,S and the outlet gas are required to be 0.02ppm H.S, the sulfur capacity is about 8%.
To remove all the hundreds of tons of sulfur a day that would be produced in crude gas from an industrially produced coal conversion plant, too much zinc oxide would need to be absorbed daily.
Therefore, to completely remove sulfur from the coarse gas, this method cannot be used.
Instead, this method is used to remove the sulfur from low-hs gas extracted from renewable desulfurization methods (e.g., Sulfiban, stretiord. Benfield, etc.).
It can reduce the concentration of H2S in the export gas to 0.02 PPM, generally 0.2-0.5 PPM.
If there is mercaptan in feed gas, to under 600 ° F to 750 ° F.
It is difficult to remove thiophene, around a temperature of 750 ° F to remove about 60%.
Since the zinc oxide adsorbent is nonrenewable, there is no significant consumption.
In this method, the raw gas may need to be heated, and the meter needs a small amount of electricity.
Basic zinc carbonate
Waste zinc oxide adsorbent contains ZnS and can be used for land filling.
In some cases, the adsorption dose of spent zinc oxide may be high enough to justify recovery of zinc.
The small knot
Zinc oxide adsorbent can dissolve H in the raw material gas;
S levels dropped below 1ppm.
It is not renewable and waste zinc oxide containing ZnS is used for land filling.
The zinc oxide is used as a protection to reduce the PPM level of sulfur in the raw gas to <1 PPM.