ENERGY EFFICIENCY AN ENERGY EFFICIENCY EVALUATION OF A BAGASSE GASIFICATION SYSTEM FOR THE SOUTH AFRICAN SUGAR INDUSTRY

SINQOBILE WISEMAN NENE NeneSW@eskom.co.za 0027 82 355 9347 PRESENTER SINQOBILE WISEMAN NENE NeneSW@eskom.co.za 0027 82 355 9347

Content Definitions Abstract & Objective Introduction Preamble on Bagasse Gasification Sugar Factory Steam / Power Generation Systems Analysis & Comparison Conclusion

Definitions Bagasse Gasification Gasifier The fibrous material that remains after juice has been extracted from a sugarcane stalk Gasification Gasification is a process whereby carbonaceous materials are converted into carbon monoxide and hydrogen by the reaction process of its raw materials at high temperatures with a controlled amount of oxygen and /or steam Gasifier A gasifier is a cylindrical enclosed reactor that is used to convert carbonaceous compounds into synthesis gas

Abstract The research was a theoretical energy efficiency evaluation of a steam and power generation system using a bagasse gasification process. The body of the research entailed a comparison between a conventional direct bagasse combustion system and a bagasse gasification system for a known steam and power generation system The findings were that a system’s thermal efficiency can be improved by utilizing a bagasse gasification system as compared to the currently used direct bagasse combustion system The thermal efficiency of a conventional system was found to be 19.69% and that of a bagasse gasification system with similar inputs to be 55%.

Objective The objective of the research was to theoretically evaluate the thermal efficiency of a steam and power generation plant for a sugar factory using a bagasse gasification system as compared to using the currently used direct bagasse combustion system in a known steam and power generation plant of a typical sugar factory.

Introduction A typical sugar factory in South Africa uses bagasse fired steam boilers for the production of steam which in turn is used in the power generation plant to generate electricity and also in the process plant for heating as part of the sugar production process. The currently used system uses a direct bagasse combustion system where bagasse if burned in a traditional boiler furnace Bagasse is used either as a sole fuel source for the boilers or as a complement for coal This system reduces the fuel cost as bagasse is deemed an almost-free fuel source as it is a byproduct in the sugar production process.

Preamble on Bagasse Gasification Gasification is a process whereby carbonaceous materials are converted into carbon monoxide and hydrogen by the reaction process of its raw materials at high temperatures with a controlled amount of oxygen and /or steam Bagasse gasification is a process whereby bagasse is gasified in a gasifier to produce gas known as syngas. The gas, after cleaning, can be used on gas turbines for electricity generation and the generator exhaust can be reused for steam generation either for a turbo-alternator set or as process steam

Sugar Factory Steam / Power Generation The factory uses steam boilers to generate steam. The Steam boilers use either coal or bagasse as their source of fuel The HP steam produced is used by Turbo-Alternators to produce Electrical Power The resulting exhaust steam is used as process steam for heating or boiling of the juice Ideally current steam plants are inefficient due to their design The need for sustainability requires maximized performance and efficiencies Maximum co-generation relies on maximum efficiency of both the steam and power generation plants

….Cont.…. The two systems under evaluation uses two different fundamental heat cycle, the Rankine Cycle and the Combined Cycle

System Analysis & Comparison The evaluation was conducted using a known system with the following quantities: Table A – Data used Table B – Calculated Values QUANTITY VALUE Bagasse Moisture (ww) 51.41 % Bagasse Brix Content/Pol Content (wrds) 1.49 % Bagasse Ash Content (wa) 4.52 % HP Steam Pressure 31000 kPa HP Steam Temperature 400 °C Exhaust Steam Pressure 120 kPa Exhaust Steam Temperature 130 °C Furnace Temperature 350 °C Feed water Temperature 100 °C Ratio of weight of air used for combustion to weight theoretically necessary 1.5 Coefficient of losses due to unburned solids (α) 0.99 Coefficient of losses due to radiation (β) 0.97 Coefficient of losses due to incomplete combustion (η) 0.90 QUANTITY VALUE Higher Calorific Value, HCV 8549.51 kJ/kg Lower calorific Value, LCV 6745.88 kJ/kg Superheated Steam Enthalpy, Hst 3227.31 kJ/kg Feedwater Enthalpy, Hfw 422.86 kJ/kg Total Sensible Heat Lost, q 300.39 kcal/kg Heat Unit Transferred to the Steam, Mv 5231.19 kJ/kg Overall Boiler Efficiency, ὴ 61.18 % Tons Steam Generated per Ton Bagasse 1.87 Ton Tons Bagasse Generated per Ton of Cane crushed 0.275 Ton Tons Steam generated per Ton of Cane Crushed 0.66 Ton CO2 Emission under these conditions 16.7 % by mass

….Cont.…. A typical gasification system: Biomass Integrated Gasification Combined Cycle

….Cont.…. Tabulated Final Analysis 19.69% 55% Quantity Value Boiler efficiency 61.18% Steam generated per ton of bagasse 1.87 tons Tons bagasse per ton of crushed cane 0.275 tons Steam generated per ton of cane crushed 0.66 tons Carbon Dioxide emitted 16.7% Total steam consumption 123TPH Total steam consumed by the power generation plant 17.64 TPH/MW Conventional System Thermal Efficiency 19.69% Gasification efficiency 55% Gasifier Thermal Efficiency 80% Bagasse consumption by the gasifier 2.84 TPH/MW Summary: Conventional System 9.549 Tons bagasse consumed per 1MWH of Electrical Power produced Gasification System 2.84 Tons bagasse consumed per 1MWH of Electrical Power produced.

Conclusion The outlined research objectives were achieved as the final analysis were able to utilise an existing plant quantities and deduce the outcome if a bagasse gasification system was to be used. The thermal efficiency for the direct bagasse combustion system and bagasse gasification system was calculated to be 19.96% and 55% respectively. It could thus be concluded that a typical sugar factory could increase its thermal efficiency by means of employing a bagasse gasification system as compared to the direct bagasse combustion system

Thank You!!!  Ikhona Imibuzo?  Postscript There is yet a lot of work to be done in the research field and the feasibility of utilizing a bagasse gasification system for an existing sugar factory as the current streams such as bagasse conveying, etc. may not be compatible to a gasification system. Thank You!!!  Ikhona Imibuzo? 