Generating Electric Power for In-house Use. Shabelle Sugar Factory is in the fortunate position of being able to generate its own electricity so that its factory is self-sufficient. The fibrous residue left after sugar-cane crushing is burnt in boilers to produce high-pressure steam. This high-pressure steam is then:
- Used to turn the factory mill turbines, etc.
- Passed through turbo-generators to produce electric power, after which the low-pressure steam is used in the sugar manufacturing process
The electric power used in Shabelle Sugar Factory is, hence, generated from a renewable biomass energy source.
The capacity of Shabelle Sugar Factory’s co-generation not only meets the entire needs of the factory and infrastructure on a 24-hr per day basis.
There is a continuing deficit in electricity generation in Ethiopia and the national utility has undertaken emergency measures to supplement generation using diesel and heavy fuel oil. Moreover, there is a growing demand for power in the country for development.
Considering this situation and the need to increase the renewable energy supply whilst conserving fossil fuels and reducing carbon emissions, the Shabelle Sugar Factory co-generation envisages installing:
- A new 160 TPH 67 bara(a) boiler
- A new 30 MW double-extraction-condensing turbo-alternator
- A new switch-yard for power distribution
- An additional new 14 km distribution line for grid supply at 33 KV
All of the new equipment will be procured shortly, and the co-generation project is expected to be commissioned by July 2019, after which Shabelle Sugar Factory will supply around 32 MW electricity to the grid for 24h/d for at least 305 days each year.
The power house has two back pressure turbo alternators having a 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 a capacity of 2×1.5 MW and 2.75 MW are installed for black start capacity and power during shutdowns as well as emergencies.
As no plant can operate without air, Shabelle 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.
Shabelle Sugar has three 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.
Shabelle 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.