Technical Session I – Problems related to Sulphuric Acid Plants
This is specific problem of PPL and is not observed in any other Sulfuric Acid plant. The process conditions of other plants may be checked by M/s.PPL.
It is suggested that castables may be replaced by bricks. M/s.SPIC suggested use of insulating bricks in place of castables.
The present MOC is SS 310 and no other material is in use.
Gland packing material fails at high temperature of more than 400 C.How- ever a 5 mm gap in the gland packing can take care of expansion at high Temperature.
It is not suggested to keep furnace gas box uninsulated instead reasons for plate becoming red hot may be found to provide necessary solution.
Yes, it is the only universal method. However, M/s.GSFC suggested that Ammonia vapour may be introduced through steam ejectors.
No insulation is required for air blowers. However, M/s.Lloyd Insulation may be contacted for any suitable insulation material.
In SPIC Incolloy 800 is used for thermo well and is suitable for temperature upto 1200 C. However, brick lining in furnace should be perfect so that thermo well has long life.
Luro burner is proprietary item and no solution to be suggested.
Sprinkling of water is the only measure. However, granular sulfur has minimum dust problems.
This problem is mainly due to ash in sulfur and the 1st objective should be to remove ash from sulfur using candle filter.
This can only be used partially in DAP plant. However this subject is under discussion in Environment Committee of FAI.
This may be shared by participants through E_mail.
It was suggested that the only solution is not to have any welding in the bellows. Bellow should be of SS316 L
Monsanto process uses burner guns for which number of suppliers are there and this may be shared through e_mail by participants
M/s.GSFC informed that in their online analyser, they are using air ejectors for charging SO2 and the basic purpose of ejector is to cool the gas. The calibration frequency is 6 months.
This can be done witrh 5% Soda lime in hot water. After this it should be dried and no pocket to be left in wet condition.
This problem occurs at low load. If concentration is more than 99% SO3 is Sucked with air and comes to duct and gets condenced. Hence, this cncentration limit care must be taken in the process. Also temperature in the IAT outlet should be above dew point.
Use of high efficiency catalyst such as BASF / Haldor-Topsoe is more reliable to improve conversion efficiency.
i) Air Filter for good quality air & mist free air from drying tower out let and use of good demister pads made up of 316L & 650 mm thickness ( supplied by Monsanto) is helpful in achieving this.
ii) Purity of Sulfur
iii) Acidic sludge in duct
M/s.PPL informed that pressure drop was limited to 100 mm even after one year operation due to above factors.
Siphoning is the only method if tank level is high and in case of low tank level, manual cleaning through manhole is suggested.
Monsanto process uses burner guns for which number of suppliers are there and this may be shared through e_mail by participants.
This may be shared mutually by participants through E-mail.
This may be shared mutually by participants through E-mail.
C. ABSORPTION AND DRYING SECTION
This problem is faced in plate coolers by all the SAP plants. However, an average life of 2 years without any problem can be expected on using Viton Gaskets.
2. What are the common problems associated with shell & tube type acid coolers?(PPL)
These are working in very well in TCL. Only tube cleaning is required once in a year.
3. Frequency of acid tower candle filter cleaning. Any commonly used method for cleaning acidic sludge of candle filter. (PPL)
Normally, candle filters had life of 5 years and cleaning during annual shut down is sufficient.
4. Can tail gas be diluted by supplying extra air in stack outlet duct if due to some reason catalyst fails to perform (to achieve the statutory limit of SO2 emission?).(PPL)
No, this is not permitted as per environmental regulations as informed by Dr.S Nand, Director(Tech.) FAI.
5. Pros and cons of trough type irrigation system and pipe type irrigation system. (PPL)
Most of the plants are having pipe type irrigation system without any problem and no comparison studies are available with trough type irrigation.
6. Vertical molten sulphur pump failure and it’s solution.(PPL)
M/s.GSFC suggested that the dirty pit height was 2.5 mtr. while pump level was 1 mtr. so that pump operation was good. However, they have overflow channel and M/s.PPL has underflow channel. It was suggested that the best remedy is to have good quality sulfur.
4 to 5 years for Filtech & Monsanto filter.
M/s. PPL informed that 316 L is the most suitable material. M/s.SPIC informed that Haste Teflon C is used by them. Life is 2 years.
It was suggested by M/s.PPL to inter change water to acid and acid to water in annual shut down. Back flushing by water provides intermediate cleaning in plate heat exchangers.
This may be shared by participants through E_mail.
Rosemond Analyser is more reliable. Also, flow should be maintained through analyser, otherwise conductivity gets disturbed
Siphoning is the only method if tank level is high and in case of low tank level, manual cleaning through manhole is suggested.
Normally, Kishore make pumps have good performance. M/s.PPL suggested that process conditions may be monitored for good pump performance that is no dilution should take place in circulation tanks which otherwise leads to corrosion and poor performance.
In case of steam turbine driven blowers it is 30 to 32 KWH/MT Sulfuric acid and motor driver blowers, it is 62 to 72 KWH / MT Acid.
It has to be 99.5% or more for SO2 to SO3 to comply to Environment regulations.
BASF & Haldor Topsoe
Chemical cleaning with 5% Na2CO3 solution in hot water and rinsing and drying completely is the usual cleanaing method.
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FAI Workshop on Operation and Maintenance Problems of Acid and Complex Fertiliser Plants
Discussion points – Technical Session II
Technical Session II – Problems related to Phosphoric Acid Plants
Rock Grinding Section
PPL faces the problem of change in the feed size of rock phosphate frequently due to use of rock phosphate from different sources, change in the blend ratio etc which lead to change in the grinding level which affects reaction efficiency.
CFL suggested that adjusting the crusher load tackles this problem to some extent. However this will have an overall effect on the plant output.
TCL & SPIC faces the problem of presence of stones in rock phosphate which affects crushing & reaction efficiency as well as wear to the balls.
It is suggested to work out the cost economics to have a pre classification section before grinding of rock phosphate.
Reaction Section
SPIC faces the problem of frequent failure of rubber lining of the reactor. Their reactors are lined with butyl rubber.
PPL suggested that carbon brick lining of reactor in addition to rubber lining will be much more effective and will be resistant to erosion also.
SPIC also faces the problem with agitators. It is suggested to have better material of construction for the agitator . However the cost economics required to be works out.
SPIC’s process is hemi hydrate recrystallisation process (HRC) and they have three digestion tanks in addition to collecting tank. Hence they have enough scope to adjust the residence time in reactor. They also use defoamer as and when required.
PPL, CFL, TCL etc also faces problems when using rock phosphate from different sources including increased P2O5 losses and defoamer consumption.
Other industries does not face this problem.
Filtration Section
GNFC uses filter cloths of poly propylene and poly ethylene for different services. The cloth is selected based on permeability.
Clarification Section
CFL and SPIC does transfer the clarifier underflow to the reactor on a continuous basis and experiences better result.
Concentration Section
IFFCO and CFL suggested that cleaning with fluosilicic acid also is effective. The presence of HF in fluosilicic acid is effective in the removal of sodium and potassium silicate scales.
Other industries doesn’t have any comment on this.
Scrubbing System
It is indicated that presence of free fluorine in the acid will lead to corrosion problems. It is very important to maintain the ratio of Fluoride to reactive silica in the reactor.
Choking of scrubber nozzles may be due to precipitation of sodium or potassium fluro silicates.
Gypsum Disposal
It is suggested to try descaling with the circulation of fluosilicic acid or dilute sulphuric acid with 2% concentration.
Cooling tower
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It was suggested that the ideal mole ratio for PN slurry is 1.40 and % solids are 80 – 83 % and temperature is about 120 C. These conditions ensures good plasticity of slurry and help granulation. .
It was suggested that the mole ratio in Dryer Pipe Reactor (DPR) may be maintained slightly above 1.0 and the height of spiral flights may be reduced to ensure proper lifting and forward movement of the material without any build-up in the initial portion of the Dryer shell..
It was suggested that proper sequence of feeding the ammonia, Phos. Acid and scrubber liquor may be maintained for stabilizing the start-up operation.
It was suggested that blending of acids and recirculation of dil. Phos.Acid can be helpful in preventing in cocking by cleaning of DPR.
One of the participant from SPIC informed that they are using minimum 47% conc Phos Acid in DPR and would like to know that if it could be further lowered. However, there was no other user using lesser conc. Of Phos. Acid.
It was suggested that the MoC of DPR should be with Teflon coating for use of conc. Sulphuric Acid..
It was suggested that the only method to prevent impingement of acid on shell was proper alignment of the feed pipe in the PN and this may be periodically checked to ensure that the acid does not spray on the shell portion of the PN.
It was informed that conc. Sulphuric Acid is added in fumes scrubber and small amount will also be added in tail gas scrubber.
It was informed that it is being done by many plants, M/s SPIC wanted to maintain pH of dust scrubber using online pH meter and this is possible but due care needs to be taken to maintain the PH meter.
One of the participant informed that the efficiency of venturi scrubber was only 80%. It was suggested that this could be improved by process control and efficiency is easily achievable to above 95%. This also is a necessity for environment compliance..
M/s PPL informed that their ammonia loss was 0.25 – 0.3 per day for production of 1200 MTPD DAP. This was considered reasonable and no one was having lower losses with PN as its reactor.
Most of the participants informed that Wilfley Pump was used and is operating effectively.
The usual method is to clean the sludge of Phos. Acid tank with water and consume this in DAP Plant at a controlled rate. For this suitable sump should be available where cleanings of Tank can be discharged and pumped to the PN.
As informed by them they have recycle ratio of 1:5 for DAP and no other user has lesser recycle ratio..
It was informed that this is not been used in any plant and only fixed speed of Granulator is maintained.
It was informed that elliptical links are used and normally 5/4 links are used in a chain.
It was informed that adjustment of SDF gates is usually manual and is varied rarely. However, air operated gates and motor operated gates are available.
It was informed that lump crusher in Dryer discharge end are operating effectively and help in prevention of oversize and lumpy material which helps in better distribution for screening and load reduction on Oversize Pulveriser.
It was informed that the oversize mesh of 3.9 – 4.1 mm and product mesh of 2.0 – 2.2 mesh was the most acceptable by most of the plants for better product sizing.
Present methods are only manual cleaning and cleaning with steam during shut down. In case of gyratory screens bouncing balls helps to avoid any build-up on the screen cloth.
It was informed that TI Diamond chains were good and also Kaneria make chains are available for elevators.
The overall experience of most of the participants were in DAP/ NPK production technology was of high standard and the operational experience were quite similar and wherever differences existed same were discussed as described above
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