Sugar is a staple in every household globally. Sugar cane is a large grass with a bamboo-like stalk sizing around 8 to 15 feet tall. The stalk contains sucrose for processing it to sugar while the other parts like leaves, top growth, and roots are considered waste. Earlier, the canes were burned in the field to eliminate the portion of the waste, preventing insects and rodents. In sugar mills, juices are extracted in the milling process bypassing the crushed cane through multiple rolls. The remaining cane after the milling process is known as bagasse. Bagasse is an efficient bio-fuel that has given rise to bagasse-fired boilers.
Understanding Bagasse as a Fuel in Detail:
Bagasse is the leftover matted cellulose fiber residue from sugar cane processed in a sugar mill. Earlier, bagasse was burned as agricultural waste. However, as the price of fuel oil, natural gas, and electricity has increased tremendously, bagasse has come to be regarded as an excellent fuel. Bagasse as fuel includes varying composition, consistency, and heating value, depending on the climate, soil type used for growing the cane, cane variety, method of harvesting, amount of cane washing, and the efficiency of the sugar mill plant. Usually, the heating value of bagasse ranges between 3,000 and 4,000 British thermal units per pound (Btu/lb) on a wet, as-fired basis, and it generally has a moisture content between 45 and 55 percent by weight.
Bagasse is primarily used in sugar mills as a fuel due to its sufficient production through combustion. It is also used for cogeneration for providing both the heat energy and electricity that is commercialized to sell as grid energy. It balances the amount of carbon dioxide by emitting the same amount of CO2, absorbed during the lifecycle of the plant, making it an environment-friendly fuel.
Production and Composition of Bagasse:
It is easy to conclude that countries producing more sugarcane produce more bagasse. One of the common characteristics of bagasse is that it contains a high moisture content of around 45-50% that is harmful to its use as a fuel. The highest producing sugar cane nations are Brazil (33%), India (23%), and China (7%). Sugar cane crushing produces about 30% mass bagasse. Five million tons of bagasse burned brings about one million tons of fuel oil saved. Therefore, bagasse is an ideal renewable biomass energy source with zero net greenhouse gas emissions.
Emissions with Bagasse-fired Boilers:
Particulate matter is the major pollutant emitted by bagasse-fired boilers, caused by the turbulent movement of combustion gases due to the burning bagasse and the resultant ash. Compared to conventional fossil fuels, the emission of sulfur dioxide (SO2) and nitrogen oxides (NOx) is lower due to significantly low levels of sulfur and nitrogen in the bagasse. The characteristics of soil like particle size can impact the magnitude of particulate matter (PM) emissions from the bagasse-fired boiler. Improperly washed sugar cane can influence the bagasse’s ash content. Neglecting combustion conditions causes increased emissions of unburned organics and carbon monoxide (CO), usually measured as volatile organic compounds (VOCs) and total organic compounds (TOCs).
Wet scrubbers and mechanical collectors are used generally to control the particulate emission from bagasse-fired boilers. Wet scrubbers primarily used for bagasse-fired boilers are impingement and venturi scrubbers. Impingement scrubbers usually function at gas-side pressure drops of 5 to 15 inches of water and are highly preferred due to their low energy requirements and maintenance issues. On the other hand, pressure drops for venturi scrubbers are over 15 inches of water. The efficiencies for both scrubbers to collect particulate matters are 90 percent or more.
Mechanical collectors are installed in a single cyclone, double cyclone, or multiple cyclone dust collectors. The efficiency for mechanical collectors to collect particulate matter is between 20 to 60 percent. The mechanical collector performance may be negatively impacted over time due to the abrasive nature of bagasse fly ash or erosion if the system is not well maintained.
Operation of Bagasse-fired Boilers:
In the last two to three decades, sugar mills have opted for bagasse-fired boilers, burning bagasse in a spreader stoker. The bagasse in bagasse-fired boilers enters the furnace through a fuel chute. It is spread across the furnace, with part of the fuel burning in suspension. The flame radiates heat to the fuel to help in combustion with the combustion area of the furnace lining with heat exchange tubes or water walls. The duration of startup for a general bagasse-fired boiler is up to 8 hours.
Bagasse-fired Boilers from Rakhoh:
As a thermal solution expert, Rakhoh Boilers understand the tremendously increasing need for sustainability. Our bagasse-fired boilers like Solid-fuel Bi-Drum, Combo X, Membrane X, and Optipac offer effective combustion with bagasse with varying product and pressure capacity.
We also provide efficient solid-fired boilers, oil-fired boilers, gas-fired boilers, biomass-fired boilers, waste heat recovery systems, thermic fluid heaters, boiler accessories, and boiler services in over 26 countries worldwide.
Explore more about our products and services at www.rakhoh.com