4.2.1) Sulphur furnace
Stop preheating: close steam to E-105 and cut the power to E-106 Close the hot air valve to the converter (by-pass of BR-101/E-107) Open the valve on air line to BR-101 before FIR-162.
Close the air inlet valve to E-105. Regulate FIR-162 at about 1067 mc/h.
Open the valve on the delivery line of P-102 to the furnace BR-101 and then close the valve on the recycling line to T-104.
Check through the sight glass SG-161 when liquid sulphur is falling down on the internal bricks and if it ignites immediately.
The furnace temperature will increases rapidly: check TIRAH-160; when it approaches to 750 °C, regulate FIR-162 to maintain it. Remember that the temperature increases when the SO2 concentration increases and vice versa. If necessary increase the air
pressure operating on PIRCAH-101.
Regulate the gas outlet E-107 temperature at 450 °C, operating with the by-pass valve of the boiler: closing the by-pass the temperature should decrease; opening it the temperature should increase.
4.2.2) Converter section
As soon as the SO2 concentration increases in the gas stream, the first bed outlet
temperature (TIRAH-182) increases, up to about 615 °C.
Start to open cooling air to the first bed outlet bringing back the temperature to 440 °C. For this operation the needed total air (FIRAL-161) will increase. Thus, increase the total air (FIRAL-161) operating on PIRCAH-101 to satisfy the quantity of needed air, keeping constant FR-162.
Also in the second bed the temperature will increase up to about 468 °C (TIR-184). Start to open cooling air to the second bed outlet bringing back the temperature to 440°C. Increase the total air flow rate as before.
In the third bed the temperature will arise up to about 445°C (TIR-186), but, opening the cooling air, it will be brought back to 440°C. Increase the total air flow rate as before. In the fourth bed, if the oxidation of SO2 to SO3 has been managed properly, the
temperature at the outlet will be around 425°C.
Check at this point the flow rate of the total air signed by FIRAL-161: It should be equal or less than value foreseen by the material balance. If it is less, add the remaining air through the line between E-109 and F-104. So open the relevant air valve to the F-104 and increase the total air flow rate up to the foreseen value actuating the PIRCAH-101. Check flow rates and temperatures adjusting them, if necessary.
As soon as the temperature at converter outlet starts to increase, open the valve on the BL-102 delivery cooling E-108 and E-109.
At E-108 outlet the process gas should maintained at about 250°C, while at the outlet of E-109 the gas temperature should be around 70 °C
At this point the total air necessary for diluting the SO3 at 4,5% concentration is
distributed among:
1) The furnace BR-101, where its quantity is regulated by the furnace temperature (750°C).
2) The three quench airs to the converter, where also is regulated by the temperature at second, third and fourth bed inlets.
4.2.3) Sulphonation Reactor
As soon as sulphur starts to burn in the furnace, it generates SO2 and then SO3 through
the converter.
The converter temperatures start to increase in the four beds.
Starting from this time, we maintain LAB in recycle for some minutes, checking the acidity continuously.
When the acidity is around 50/60, open the bottom valve of T-201 and close the T-204 bottom valve.
Now we are feeding fresh LAB to the reactor head, always collecting the reactor bottom in the T-204 tank.
Check continuously the acidity.
After 20’ the sulphonation reaction should have reached 70-80 and the reactor outlet can be switched to LG-203 and R-203.
In this way we will have collected in T-204 about 500 lts. of a mixture LAB/LABS about 50/50 which will be recovered little by little later.
Check continuously the acidity.
Prepare the suction and delivery line of the P-202 pump for sending LABS to the storage.
Open water to R-203 jacket and then also steam just to heat the jacket for maintaining the LABS at about 50°C.
Close the outlet valves of R-203 leaving LABS coming out from the higher outlet. Start R-203 stirrer.
When LABS overflows from R-203, start P-202 and regulate the level by LIC-201. Check always acidity.
The final acidity should be around 170/180. To adjust this value operates only with small variations of the LAB flow rate followed by acidity checks. Never touch the sulphur flow rate.
Open suction and delivery valves of pump P-203, start the pump and regulate FI-201 at about 7 lts/h (0,05% ).
Open cooling water to E-202. TI-207 should be around 30/35°C.
4.2.4) Exhaust Gas Treatment
4.2.4.1 Electrostatic precipitator
The operation of the electrofilter is very simple. The gas is passing now through the filter.
Adjust the voltage to a value a little below that at which the electrical discharges start. During the operation if there are frequent discharges or even a continuous arc, the voltage drops and hence the filtering efficiency decreases: the voltage must be reduced by hand until the discharges cease.
On the other hand, an attempt should be made from time to time to increase voltage in order to restore filtering efficiency, which may be reduced if the filter is dirty.
During the operation the ESP is automatically cut out, ceasing to operate, and gives an acoustic alarm if:
-the transformer oil temperature exceeds the permissible level
-there are frequent high intensity discharges (sign of excessively high voltage). -voltage at filter is too low (sign of short-circuit in the filter).
-the filter current is too high.
4.2.4.2 Scrubber
SO2 contained in the exhausted gas is now arriving to the scrubber.
From material balance we get that at 50% capacity the plant produces 17,7 x 0,5 = 8,85 Kg/h of 100% sulphite which at 10% concentration gives 88,5 Kg/h (about 80 lt.) of solution which we must be sent to the storage. So regulate manually the FI-302 at about this value, transferring this hourly amount to the storage.
Set back the ph to the previous value (7,2-7,5 ): P-302 will stop and it will start again when the ph will reach this value.
4.2.5 ) Interlock System
The interlock, which was excluded at the beginning of the start-up phase, must now be again included.