Napier grass is becoming a popular biomass for gasification process to generate electricity in Thailand. Government office also issued the project that subsidizes napier grass as raw material for power plants.
The critical factors for Napier grass for power plants projects are harvesting of the grass, moisture content in the grass, transportation to the preparation factory, and making the dried grass into pellet form or else to be able to use in the reactor of gasification process.
Muddy area can be problem for harvesting and the moisture content in the grass can be as high as 70% (not included the water from rain if the case), causing high cost to dry the grass. Transportation cost and pelletizing cost are also to be considered too. Raw material preparation process includes;
Biomass chipper/cutting Biomass material: Sugar cane stalks or Napier Grass stalks or similar can be mixed and used in most gasifier. Also woody biomass like wood chips or coconut shells can also be used but they might require a chipping or good cutting technology.
Sample of Output chip/strand size required:
Preferred: sum of average chip/strand dimensions (L + W + H) at 50 mm
Maximum: sum of average chip/strand dimensions (L + W + H) at 75 mm
Moisture content input biomass from 50-70% (by weight)
Throughput: minimum 5.0 tph fresh biomass per unit for 1 MWatt power plant size. Auxilliaries: (i) dust collection system. (ii) dust storage system.
Biomass Drying Unit Technology type: Rotary dryer or Columnar type dryer
Fuel: Biomass (grass itself, wood chips, waste wood), LPG, also Drying heat source: ambient air diluted hot gen set exhaust. Direct gen set exhaust will be between 430 and 470 Deg C and we will dilute down temperature with air to required dryer operating temperature.
Chip/strand size input: Expected Average: sum of average chip/strand dimensions (L + W + H) at 50-75 mm
Expected Maximum: sum of average chip/strand dimensions (L + W + H) at 100 mm
Moisture content input biomass (maximum 70% moisture content; target output moisture content at maximum 18-20%
Auxilliaries: (i) feed system (ii) discharge system.
This is just sample idea about the raw material preparation and gasifier related machines.
The bolt screw counting and feeding system to connect with bagging unit (automatic packing unit). Using vibration generator unit (single phase vibration generation and control unit) and sensor + PLC for the counting unit.
Biomass Shredder/crusher (Small size)
In the video is a small, movable machine to shred the green biomasses (i.e. napier grass, stems, green leaves, etc).
เครื่องบดสับหญ้าพลังงาน หญ้าชีวมวล และเชื้อเพลิงเขียวประเภทต่างๆ
Last year (2012), Thai government announced about Napier Grass for generating electric power as follows.
“The government will issue guidelines within the next two months on a policy to promote generation of electricity from Napier grass, Energy Minister Pongsak Ruktapongpisal said yesterday.
Napier grass, originally from Africa, is also known as Uganda grass or elephant grass for being a favourite food of elephants.
Speaking on the sidelines of the “Green Energy Forum: A Balancing Act for Sustainability” held by Krungthep Turakij, Pongsak said Germany had developed 7,000 power stations fuelled by Napier grass that provided 7,000 megawatts, and Thailand could match that production.
The ministry will provide a “feed-in tariff” subsidy of Bt4.50 per kilowatt-hour (unit) for a period of 25 years to power plants that use as feedstock Napier grass supplied by local communities. This grass can be grown in many parts of Thailand, especially in areas currently used as sugar-cane and tapioca plantations in the Northeast and Central regions, provided they are situated not too far from the power grid, he said.
Pongsak said alternative energy currently contributed merely 1 per cent of Thailand’s electricity production, and Napier grass would contribute a significant chunk of the target to increase the contribution of alternative energy to 25 per cent within 10 years.
“Concerning energy security, we are currently depending on natural gas for as much as 67 per cent [of power-generation needs]. Seven new records of peak power loads occurred during the past year, which prompted a call to save energy. While our installed capacity is 32,000MW, the power demand peaked in May at 26,774MW, leaving a power reserve gap of only 16 per cent,” he said.
Pongsak said that if electricity-use growth rates remained at the current level, there could be power-supply issues in the next two years. Investors have often asked him about the government’s plan to boost electricity capacity.
He said the government would negotiate with Myanmar to pursue the 7,000MW Salawin hydropower project as well as putting more emphasis on biomass and biogas, including electricity production from Napier grass.
Considering the Bt6.50-per-unit subsidy for solar farms, promoting more solar plants will place an heavy burden on the public in terms of higher electricity costs, the minister said.
The question is if this project is really economical or not. Many people have heard about some of the Napier grass to feed (“Elephant grass”). Can it be used as a fuel briquette (Briquette) or pellet (pellet)? What are the pros and cons of napier grass?
Napier grass really worth the fuel used to produce energy or not ? Depends on several factors. Particular grass species (Pakchong 1, Emperor, etc. ), which can grow well in the terrain and climate , which is used as fuel. It should be planted so the moisture at the harvest is minimal, enough texture of grass ( 3-4 months , humidity is about 65-70 % by weight). Harvesting (labor, machine) and Transportation to the factory is also a factor to consider too .
The key factors for using Napier grass to make into briquette or pellet form are the preparation of fresh grass into the form ready to be briquetted or pelletized because this process requires a lot of energy. By pressing the water out as the crushing roller, cut the grass into smaller sizes to increase the heat transfer area, the grass still needs drying whice requires a lot of energy, especially to dry grass to reduce moisture from 65-70 % to 15-20 %. First, the grass is being pressed by rollers, which can reduce the initial moisture content down to approximately 35-45 %. Using conventional type rotary drum drier, the required amount of fuel is very high because of low efficiency (in most cases, inevitable to use biomass fuel, i.e. napier grass itself). More efficient process is to use superheated steam, which can dry the grass quickly and the grass does not have chance to catch a fire compared with the conventional hot air type.
Coal Pellet machine (30 HP, TWP-03FCP Type) can pelletize about 500-600 kg/hr, depending on the size and moisture content of coal. The pellet diameter can be adjusted from 6 mm. to 15 mm. (need TWP-04 or higher model). Length can be adjusted by length adjusted unit, installed at the machine.
Coal pellet can be sold at higher price than undersize coal or fine coal. Higher moisture content in the pellet is acceptable in most cases (water may be needed for moisture content adjustment for pelletization process).
Fine Petroleum Coke – Pellet making test by small machine (7.5 HP)
The sample is very dry. Using small machine could not press successfully. It requires water or binder to help improve pellet forming and strength.
If using higher power motor, this would help improve the forming and process-ability.
1. What is the standard moisture level in the charcoal?
2. How to calculate or measure the moisture content before selling/export?
3. Do you have any easy way to check if the moisture content is o.k.?
Basis of calculation: % Moisture ( wet weight ) = (weight of charcoal – dry charcoal) x100 /starting charcoal weight.
4. If we have high-tech tools to measure the moisture, what is the favorable level for charcoal / charcoal briquette export.
Please kindly reply
Normally, the charcoal / charcoal briquette moisture content should be in range of 7-10 %. However, there are some differences between charcoal (wood charcoal) and charcoal briquette.
1) If the charcoal manufacturer use water to extinguish the fire, then it would be somewhat higher moisture off the stove than to extinguish by closing the kiln, which almost no moisture left. Anyway, Usually charcoal will absorb the moisture in the atmosphere soon after you remove the charcoal from the kiln. If you do not put water directly to stop the carbonization (stop the charring), then the moisture content will not exceed 10%.
Other categories, such as mangrove charcoal imported from Myanmar , most of it will be humid because the sea water or sea water splashing into the boat. The salt is very rich in charcoal.
Ever is the time to send them to the destination. Countries with low humidity, like the Israel, the weight after 1 month storage can loose more than 5-10% in dry season. It has been my experience with clients who have experienced this but they were already aware of this problem at first (that is what I was told).
Conclusion is that rarely do they make it much moisture. But we can check easily and to be aware of is the time to pack a bag or box . If too damp can cause rot box or bag wet . You can test by packing and taking the box/bag under the sun and then, after back into the shade and cooling, open to check it.
Because containers can reach reach 60-70 degrees Celsius during shipping, if travel long distance like to Europe it will be more than 1 month, extreme heating/cooling will cause the problem.
2 ) Charcoal briquette with moisture higher than 10 percent moisture, it will become softened and mushy after a 1-2 day after packing. Thus, carry out a test (same as charcoal case), it is not difficult to know that the humidity is low enough or not.