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

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

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

4. 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

5. 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%.

6. 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.

7. 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.

8. 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

9. 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

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

11. 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
kJ/kg
Lower calorific Value, LCV
kJ/kg
Superheated Steam Enthalpy, Hst
kJ/kg
Feedwater Enthalpy, Hfw
kJ/kg
Total Sensible Heat Lost, q
kcal/kg
Heat Unit Transferred to the Steam, Mv
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

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

13. ….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.

14. 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

15. 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? 