1.Features and Scope of Application
T306 Zinc Oxide Desulfurization Adsorbent, developed by the Northwest Research Institute of Chemical Industry, is applicable to desulfurization of residue cracking gases or syngas and purification of feed gases for organic synthesis processes. It is suitable for both higher (350--408℃) and lower(150--210℃) temperature use. It can convert some simpler organic sulfur while absorbing inorganic sulfur in gas stream.
Main reaction of the desulfurization process is as follows:
(1) Reaction of zinc oxide with hydrogen sulfide
(2) Reaction of zinc oxide with some simpler sulfur compounds in two possible ways:
a. Organic sulfur compounds, catalyzed by zinc oxide, react with hydrogen to form hydrogen sulfide:
CS2 + 4H2 = CH4 + 2H2S
C2H5SH + H2 = C2H6 + H2S
Then hydrogen sulfide is absorbed by zinc oxide
b. Zinc oxide reacts directly with organic sulfur compounds
COS + ZnO = ZnS + CO2
T306 is an ideal desulfurization adsorbent for deep purification cases, especially those at higher temperature (350--400℃).
4.Normal Operation Condition
Feedstock : synthesis gas , oil field gas, natural gas, coal gas. It can treat gas stream with inorganic sulfur as high as 2-3g/m3 with satisfactory purification degree. It can also purify gas stream with up to 20mg/m3 of such simpler organic sulfur as COS to less than 0.1ppm.
Normal operation condition is as follows:
Loading depth: Higher L/D (min3) is recommended. Configuration of two reactors in series can improve utilization efficiency of the adsorbent.
(1)Clean the reactor before loading;
(2)Put two stainless grids with smaller mesh size than the adsorbent;
(3)Load a 100mm layer of Φ10—20mm refractory spheres upon the stainless grids;
(4)Screen the adsorbent to remove dust;
(5)Use special tool to ensure evenly distribution of the adsorbent in the bed;
(6)Inspect uniformity of the bed during loading. When inside-reactor operation is needed, A wood plate should be put on the adsorbent for the operator to stand upon.
(7)Install A stainless grid with small mesh size than the adsorbent and a 100mm layer of Φ20—30mm refractory spheres at the top of the adsorbent bed so as to prevent entrainment of the adsorbent and ensure even distribution of the gas stream.
Note: Evenly distribution of the adsorbent is essential to its efficient operation, which should be paid close attention to.
(1)Replace the system by nitrogen or other inert gases until oxygen concentration in the gas is less than 0.5%;
(2)Preheat the feed stream with nitrogen or feed gas under ambient or elevated pressure;
(3)Heating speed: 50℃/h from room temperature to 150℃ (with nitrogen) ; 150℃ for 2 h (when heating medium is shifted to feed gas ), 30℃/h over 150℃ until required temperature is attained.
(4)Adjust the pressure steadily until the operation pressure is attained.
(5)After pre-heating and pressure elevation, the system should first be operated at half load for 8h. Then raise the load steadily when operation becomes stable till full-scale operation.
Cut feed gas (oil) supply. Close inlet and outlet valves. Keep the temperature and pressure. If necessary ,use nitrogen or hydrogen-nitrogen gas to maintain the pressure to prevent negative pressure.
(2 ) Change-over of desulfurization adsorbent
Close inlet and outlet valves. Steadily lower the temperature and pressure to ambient condition. Then isolate the desulfurization reactor from the production system. Replace the reactor with air until oxygen concentration of ＞20％ is attained. Open the reactor and unload the adsorbent.
(3) Equipment maintenance (overhaul)
Observe the same procedure as shown above except that pressure should be lowered at 0.5MPa/10min and temperature lowered naturally.
The unloaded adsorbent shall be stored in separate layers. Analyze the samples taken from each layer to determine status and service life of the adsorbent.
8.Transportation and storage
(1)The adsorbent product is packed in plastic or iron barrels with plastic lining to prevent moisture and chemical contamination.
(2)Tumbling, collision and violent vibration should be avoided during transportation to prevent pulverization of the adsorbent.
(3)The adsorbent product should be prevented from contact with chemicals during transportation and storage.
(4)The product can be stored for 3-5 years without deterioration of its properties if appropriately sealed