for Sulfurous Gas Oxidation Catalysts
For the efficient work of the catalytic reactor one shall use , as a rule, two types of the catalysts: high-temperature ( for operation in the temperature range 460-610 ˚C ) and low-temperature ( for operation in the temperature range 380-460 ˚C ). The qualitative ratio of the catalysts shall be determined , first of all, depending on the composition of the processed gas. Combination of different types of catalysts are successfully used at sulfuric-acid plants.
The most important properties of the catalysts are interdependent, thus one and the same factor may influence a number of properties, changing them to opposite. The choice of form and size of the catalyst grain shall be determined through a compromise between the desire to reduce the influence of the intradiffusion deceleration , declining together with decreasing the ratio of the grain volume to its surface , and not to exceed the permissible value of hydraulic resistance, increasing with reduction of the grain size and unconfined space between them.
These instructions should be considered as general guidelines for starting up a SO2 converter.
Specific issues such as valve positions, converter, gas bypass options, safety interlocks, etc. are not included here . Specific issues should be provided documentation project sulfuric acid plant.
SVD ( Ê D) – a general-purpose catalyst :
- operates within the range of temperatures 390-640˚C and sustains short-time increase of temperature up to 650˚C; is good for application in all layers of the catalytic reactor (KA);
- shows high stability under varying loads;
- sustains long stops of the catalytic reactor , does not require additional attention and care when operated in harsh environment ;
- Ignition temperature - 360 ˚C.
SVNT ( Ê D) – low-temperature catalyst :
- together with properties attributable to SVD ( Ê D) ensures increase of reactivity when used in the 2 nd , 3 rd , 4 th and 5 th layers , when being fed to the upper part of the 1 st layer ensures operation under low temperatures at the input;
- is intended to provide for high reactivity when sulfuric anhydride prevails and the temperatures are lower than in the upper layers;
- improves conversion under standard charge ensuring increase of reactivity by 25 % more than SVD ( Ê D) catalyst , and enhances efficiency;
- ignition temperature 3 6 0˚ C.
SVD ( Ê -D, Ê ) – cesium promoted catalyst , has lower melting temperature and as a consequence reduction of ignition temperature , is intended for operation under low temperatures :
- ensures increase of conversion level when charge to bottom layers and , as a consequence, increase of efficiency with regard to acid , reduction of SO 2 emission ;
- lower temperatures at the layer input;
- reduction of time for starting reaction;
- improved performance under high temperatures;
- resistance to low-temperature deactivation;
- ignition temperature SVD ( Ê -D, Ê ) 330 ˚C ( activation 330˚C).
- charged to 3 rd , 4 th ,5 th layers of the catalytic reactor with single contacting , 4 th , 5 th layers- double contacting, into the upper part of the 1 st layer – in case of the lowest temperature at the input , into the other layers – in case of the input temperature of 390˚C.
SVD ( Ê -D, Ê ) SP - Super Cesium promoted
It is used in the last bed of a converter; maximum conversion is achieved.
Ñylindår – general catalyst grain form, has increased surface / grain volume ratio :
- ensures efficient gas distribution in all layers of the catalytic reactor;
- show high mechanical strength , less susceptible to wear and fragmentation, providing for longer service life and less losses in the course of sieving ;
- granule dimensions allow to control pressure difference in the catalyst layer.
Ring - this form of the catalyst ensures more gas flow :
- allows to reduce pressure loss ;
- provides for uniform distribution of pollution , bringing about reduction of growth of the hydraulic resistance;
- contributes to less frequent re-screening of the catalyst even if highly polluted gases are used ;
- can be used in all layers.
Star Ring - the form is developed for the 1 st and 2 nd layers of the catalytic reactors , however, may be effectively used in all layers of the catalytic reactor:
- ensures high reactivity and sufficient mechanical strength;
- allows to reduce hydraulic resistance to maximum through increase of the fractional void volume.
Packing, Storage, Transportation and Handling
The sulfurous gas oxidations catalysts shall be supplied in the air-tight closed packages ensuring safety of the catalyst while in storage and transportation.
The catalyst shall be kept in closed packages, in dry premises, shall be protected from moisture.
The catalyst shall be transported in covered railway wagons or trucks in accordance with the Cargo Carriage Rules for such transportation means.
The package (drums, barrels, etc) with the catalyst shall be loaded upright and the bags – aflat.
When handling the catalyst one shall take precautions not to destroy the packing, not to break the grains , one shall not execute operations which may bring about dust formation and use ventilation if necessary.
Recommendations Prior to Charging:
Prior to charging of the catalytic reactor one should:
- examine integrity of lining , metal constructions and distribution devices;
- fulfill hydrostatic test of the reactor and the heat exchanger;
- check horizontality of packing and safety of fixture of the supporting net of stainless steel or ceramic checkerwork. If quartz (intallocs) is charged, then the size of pieces shall not exceed 20x20 mm , height of quartz (intallocs) layer --100mm.
- Calculate and make up the charging schedule (quantity of the catalyst, type of catalyst, granule form).
- Before the delivery of the catalyst to the hatch-manhole. The catalyst of large containers of a volume of 127 litres through the tray-sieve overload in container volume is 25 to 50 liters
- Tray with a mesh simultaneously performs the function:
- removal of damaged during the transportation of a catalyst
- move the catalyst of containers 127 litres.
Container 25 to 50 liters convenient for transportation through the Converter and the subsequent uniform placement of a catalyst in a layer
- Tray size of about 500 to 1000 mm. Mesh with a mesh size - 8 mm, length of the cell 8 - 100 mm
- Catalyst is first emptied from the opposite side of the manhole. Pour evenly from the packaging to the desired layer height
Charging (discharging, sieving) shall be effected in such a way so as to reduce the time of exposure of the catalyst to atmospheric impact.
This is connected first of all with the fact that sulfurous gas oxidation catalysts are hygroscopic and so it shall be prevented from ingress of moisture and rain.
When charging the catalytic reactor one shall observe uniformity of distribution of the catalyst in terms of the layer height and reactor section.
In the course of charging the upper layer of the catalyst is leveled off with scrapers ( wooden or otherwise) .
Not to damage the quartz and catalyst during charging when moving along the layer , it is necessary to put the ladders .
After charging and examination of the layer the hatch is closed.
Catalysts show high stability in the course of heating and so quick heating does not influence its properties.
Heating rate of the catalyst and catalytic reactor shall be determined by the rate of heating, allowed by the standard technical documentation.
Temperatures of the flue gas and hot air of the heater are specified by the technical documentation. During start-up, the initial heating of the converter should be carried out using dry air to minimize the water condensation on the catalyst. With the assurance that the air is dry, blow the air through the converter and heat the catalyst beds until the outlet from each layer is at least 120°C (SO3/H2O dewpoint).
When reaching the temperature of 120 0 C in the layers the catalyst reactor shall be conditioned within 2-3 hours to eliminate moisture, absorbed by the catalyst when the catalyst reactor is stopped or when the catalyst is re-sieved.
A standard preheating temperature gradient for catalyst is approx. 20 ̊ C /h. Very important that the first pass inlet temperature does not exceed 530 ̊ C while the process gas does not contain SO2 to prevent desulfation of the catalyst. Continue heating until the following converter temperature: layer 1 – 460 ̊ C layer 2 – 430 ̊ C layer 3 – 430 ̊ C layer 4 – 420 ̊ C.
The sulfurous gas oxidations catalysts in the course of production is in sulfatized state and does not require saturation , so when starting up the catalyst reactor initial SO 2 concentration may reach 5-7%. After that the temperature mode of the catalytic reactor is increased till it reaches the working temperature.
The specified working temperature is set through change of gas load and concentration SO 2 .
The sulfurous gas oxidations catalysts shall not be used for long time under the temperatures higher than 640-650 0 C .
For sustained operation it is not recommended to reduce temperature at the layer input lower than the ignition temperature.
Prior to the shutoff the catalytic reactor shall be heated up to the highest temperature range (specified by the schedule). After the shutoff the load valve shall be closed.
Stoppage of the Catalytic Reactor for Repair
When stopping the catalytic reactor for a long repair it is necessary to blow it down from SO 3.
Prior to blowing the temperature shall be maximized . Blowing shall be done with air. One shall not allow sulfurous and sulfuric anhydrides ingress into the reactor. Output temperature shall not be lower than the temperature of sulfuric acid condensation.
Blowing is considered completed when there is not any SO 3 in gas.
- Before discharge the catalytic reactor shall be blown down from SO 3 and cooled.
- It is necessary to ensure that atmosphere inside the reactor is safe for personnel.
- It is recommended to discharge the catalyst manually , this reduces the catalyst failure , allows to divide the catalyst from the supporting media thoroughly.
- When charging two types of catalysts it is necessary to discharge them separately . If the upper layer is charged without using dividers , then to separate it when discharging one shall accurately measure the depth.
- The layers which shall not be discharged shall be protected from atmospheric air ingress and waste from the upper discharged layer
- Discharge of the catalyst using vacuum shall safe a lot of time and effort , however, the catalyst losses increase. To reduce such losses the length of sleeves and pipes for the downstream air flow and catalyst shall be as short as possible.
- To ensure low losses one shall use non-metal sleeves , avoid sharp bends of pipes when installing the vacuum device.
The sulfurous gas oxidations catalysts may be sieved and used more than once , cause they have good resistance to wear. Non-stop operation between sieving two years and more.
It is necessary to analyze the sieved catalyst with regard to catalytic reactivity and mechanical strength.
The catalyst prepared in such a way shall be charged to the respective layer and above it the fresh catalyst which makes up for the losses of discharging and sieving is charged.
The manufacturer may conduct for the enterprises which use the sulfurous gas oxidations catalysts SVD( Ê D),SVNT ( Ê D), SVD( Ê -D, Ê ), the following types of maintenance:
- study of the state of the catalytic reactor;
- calculation and making up of the charging schedule;
- calculation of the most efficient operation modes ;
- recommendations on elimination of faults.
The dust of catalysts may be introduced into the body through the inhalation organs, skin and digestive organs.
The persons working with the sulfurous gas oxidations catalysts shall be equipped with personal protection means for protection of skin , inhalation apparatus and with the special-purpose work wear in accordance with the standard norms.
For protection of the inhalation organs one shall use the respirator , for hands- gloves. The requirements of personal hygienic measures shall be strictly observed.
With the purpose of protection airproofing of the equipment and communication shall be ensured.
First aid measures: in case of contact with skin or eyes – rinse with water