Ship Unloading and Storage
Ships deliver raw sugar from various origins to USC berth at Jeddah Islamic Port (JIP). Two grab crapes (with total capacity of 800 tons/hr.) unload the cargo to the conveyors to store the sugar in two A frame raw sugar sheds with a total capacity of 100MT. These sheds have underground conveyors transferring the sugar to the melting stage.
The Refinery dispensed with affination of raw sugar in 1999 with the advent of very high pol (VHP) raw sugar. Raw sugar for processing is directly from the storage sheds via a 50 K ton supply bin. Melting is preceded by delivering sugar via two measuring scrolls. The raw sugar is discharged in parallel into two stirred tanks, in which the brix of the melt is controlled via a density controller by the addition of sweetwater. Temperature control is achieved by high volume recirculation of first stage melt through an externally situated direct contact vapour heater, using vapour 2 from the evaporator. Final melt discharged from the last stirred tank via two mass flow meters and pumped away to the carbonatation station.
|Melt rate||160 tph|
|Melt brix||62 - 65|
|Melt temperature||80 deg C|
|Melter capacity||105 m3|
|1st stage Recirculation rate||450 cu m/hr|
|Melt residence time||30 minutes|
Raw melt is limed proportionally at a rate of between 0.40 % and 0.60 % CaO on melt brix prior to carbonatation. The carbonatation station consists of two or three sets of first and a second stage. The former is arranged in parallel. The discharge from the last stage is pumped into a contact heater raising the temperature of carbonatated liquor back up to 85 deg C employing vapour 1.
Boiler flue gas with a carbon dioxide content of 10 % to 11 %, after having been scrubbed clear for sulphur dioxide (SO2) , is compressed and fed proportionally to the saturators. The first stage saturators handle 80 % of the limed melt gassing, with 20% taken by the second stage. Gas rate adjustments are made according to the final pH level in each saturator stage. Lime dosing rate is determined by filtration efficiency and colour quality of the filtered liquor.
|Carbonated liquor pH's:-|
|pH out of 1st Stage||9.5 to 10.0|
|pH out of 2nd Stage||8.3 to 8.5|
|Total saturator capacity||200m3|
|Total liquor residence time||50 min|
|Gassing rate||60 - 70 cu m/ton melt solids|
Liquor from carbonatation is filtered through 12 Gaudfrin filters. Each filter has multiple vertical leaves, fitted with sewn on stable fibre woven polyamide filter cloths. The automatic control system adjusts the operating pressure of the filter to give constant flow and stops the filter cycle at a preset pressure. The cloudy liquor from the start of a filter cycle is recycled back to the main melter. The clear liquor is sent forward to the granular activated carbon plant for further decolourisation. The performance of the filter cloths is maintained by washing with sulphamic acid when flux drops offs.
The sluiced cake from the Gaudfrin filters is collected and filtered in 2 plate and frame presses. The sweet water generated in this process returned to the main melter. The discharged cake is transported to landfill sites
|Filter Supply||1000 - 1200||62 - 65||0.10 - 0.15||8.5 - 8.8|
|Filtered Liquor||700 - 900||61 – 64||0.10 – 0.15||8.3 – 8.7|
|Press water||20 – 25||1.0 – 2.0||6.5 - 7.5|
Granular Activated Carbon (GAC)
Filtered liquor from carbonatation after filtration is decolourised by being passed in series through two stages of activated carbon columns. The plant consists of 9 pairs of vessels of which seventeen are on decolourising duty, with one being regenerated at any one time. The columns are rotated from lead to trail arrangement in order to obtain maximum decolourization. The total cycle length is approximately 400 hours depending on the input colour of the carbonated filtered liquor.
The vessels are all carbon steel 60 cu m Volume and contain 50 cu m granular activated carbon. The exhausted carbon is washed out of sugar and ready for regeneration
GAC regeneration is achieved by heating in a multiple hearth furnace in the absence of oxygen and increasing temperatures from top hearth to bottom hearth ranges between 200°C to 950°C . The carbon is transported by water to a receiving tank where it is separated from the transportation water.
After the dewatering process, the moist carbon is fed to the top of the hearth after being dewatered in a vacuum filter belt. Rakes on the central shaft direct the carbon to the center where it falls by gravity through a hole to the hearth below. The glowing carbon is then quenched with water and transferred back to fill new column by turn
The flue gases contains fine particulates of carbon and abnormal quantities of carbon monoxide is sent to an incinerator (after burner) to complete oxidation of the carbon monoxide and carbon fine particulates into carbon dioxide and water in oxygen rich environment at 650°C
After passing through the de-colorizing plant, the liquor is termed fine liquor and is sent forward to the evaporator.
Operational data (per ton carbon reactivated)
|Carbon Loss||Kg||50 - 60|
|Fuel inc after burner||liters||400|
|Temperature from top to bottom hearth||°C||200 – 950|
The evaporator station consists of three falling film units arranged as a double effect with a forward flow configuration. Two vessels make up the first effect, while the single remaining unit the second effect. Steam is arranged in parallel while the liquor passes in series. These units raise the fine liquor brix to 73 deg. The evaporator output is pumped to the white pan station for crystallization.
|Effect 1 surface area||2100|
|Effect 2 surface area||500|
|Vapour 1 Pressure||0.75 bara|
|Vapour 2 Pressure||0.50 bara|
United Sugar has two types of crystallization, batch and continuous:
The batch crystallization stage consists of six stirred calandria pans of 57.5 cu m capacity. The boiling scheme is the normal 4 or 5 boiling system, with all sugar being mixed after going through the dryers and the final jet (return syrup) is then sent to the Recovery House for further exhaustion. The six batch pans are heated with exhaust vapor at 1.2 barg pressure. The boiling cycle on all pans is automatically controlled using microwave density meter and DP level transmitters giving input signals to the DCS system. The final strike brix is set by the stirrer power consumption.
The continuous pan is a BMA VKT, which is powered by V1 at 0.75 bara. The continuous pan consists of four compartments. Each compartment is provided with an agitator, the first two compartments with three bladed impellers and the last two with five bladed propeller stirrers (figures 2 and 3). The first two are driven by a 37kW motor, while the last two compartments are served by 90kW motors. Final brix control in chamber 4 is provided by amps draw-off of the stirrer motor. Chamber three also has a 90kW motor in the event that compartment is off line for cleaning.
Seed for this pan is prepared by slurry seeding a batch pan and metering a 0.4mm crystal into the first chamber of the VKT. The final crystal size is 0.7mm and a crystal content of 55%.
Size of sugar crystals can be controlled during crystallization by controlling quantity of seed and crystallization time given for the super saturated sugar syrup to produce sugar with different sizes as per request (extra fine sugar, fine sugar or coarse sugar)
|Conc Fine Liquor||0.1||150 - 200|
|Jet 4||2-3||7,000 – 10,000|
|R1 Sugar||0.001||15 - 20|
|R2 Sugar||0.002||30 - 40|
|R3 Sugar||0.004||60 - 80|
|R4 sugar||0.008||80 - 160|
|Extra fine sugar size (MA) mm||0.35|
|Fine sugar size (MA) mm||0.60|
|Coarse sugar size (MA) mm||1.20|
White massecuite from the pans is discharged into horizontal stirred cylindrical 70 cu m strike receivers, one for each pan. These in turn feed the white sugar centrifugals which are likewise arranged in separate bays dedicated to each pan. Currently there is a mix of different makes of centrifugals consisting of nine Silver Weibull automatic batch machines and five BMA automatic machines.
The wet sugar discharged from the centrifugals is transported by screw conveyors to 5 rotary louvre dryers. After drying, the sugar is weighed using a belt weigher. The sugar is stored in two conditioning silos of 8500 MT each.
United Sugars conditioning facility consists of two silos of 8,500 tons holding capacity. Conditioned sugar is fed two different packing stations, one industrial and the other consumer packing plant.
Dried refined sugar is conditioned by passing it in plug flow counter current with filtered dehumidified air. The air is dehumidified by means of refrigeration. Optimum residence time required to condition the sugar is approximately 72 hours.
|Sugar inlet temperature||45 – 48 deg C|
|Inlet air temperature||40 deg C|
|Inlet air humidity||30% RH|
|Inlet sugar moisture (Karl Fischer)||0.08 %|
|Outlet sugar moisture (Karl Fischer)||0.04 %|
The power house has two back pressure turbo alternators having capacity of 9MW each and operating at high pressure steam. The turbo alternators also supply the required exhaust steam 1.2bar @120⁰C (low pressure steam) uses by the process.
The high pressure steam 41bar@380⁰C is supplied from two oil fired boilers each having a capacity of 110 tons/hr. The total installed capacity is some 40 % in excess of present process plant requirement for a 155 tons/hr melt rate.
Three Diesel generators having capacity of 2x1.5 MW and 2.75 MW are installed for black start capacity and power during shut downs as well as emergencies.
As no plant can operate without air, united sugar has also seven air compressors with different capacities to fulfill the requirements of moisture and oil free instrument air and utility air around the facility.
United sugar has three sea water desalination units capable to produce 2400 cu meters of water per day with TDS of 15ppm maximum and 6.5-7.5 ph.
All the units are thermo compression multi effects type operating at medium pressure steam 14 bar @ 230⁰C. Production of these units fulfills all the water requirements of the company.
Through various processes, this water consumes as boiler feed water, process water, firefighting water, cooling water, domestic water …etc.
Effluent water treatment plant
The raw waste water is sent to the equalization basin for temporary storage of waste water. The equalized waste water is pumped to the cooler then neutralized in the neutralization pit. The effluent is then subject to aeration in an activated sludge treatment plant which has built in clarifiers. The clarified effluent is then sterilized and filtered in pressure filters in order to remove any remaining suspended solids. The unit includes also an oil/water separation system, a foul water system.
Flue gas scrubbing
The carbon dioxide CO2 that is needed to react with the lime is obtained from the boiler flue gas with a content of about 10 % after scrubbing with sea water and soda solution, to cool it, to reduce its volume and to remove fly ash, soot and other solids and corrosive gases. The gas is pumped to the carbonatation station via four liquid ring compressors.
Boiler water treatment is consisting of a demineralization process based on mixed bed ionic exchange resins of 60m3/h capacity.
Cooling water plant
Cooling water for the plant is supplied by a system composed of a cooling tower and a closed circuit in which clean water circulates. The closed water circuit is provided by side-stream filtration to remove suspended solids. A chemical dosing system is implemented to prevent scaling and corrosion.