To produce biofuel, Micronex Systems Inc is able to process the following feedstock materials:
- Empty Fruit Bunches (EFB or Palm Waste)
- Deinking Sludge
- Wood Chips, Bark
- Biosolids (Sewage Sludge)
- Animal Manures
In Asia, plantations which produce palm oil have large quantities of palm waste known as Empty Fruit Bunches (EFB). In its raw state, EFB is both very fibrous and has a high level of moisture content. When processed into powder it becomes excellent biofuel for power boilers.
To dry and shred the EFB, FASC Malaysia installed a modified version of the KDS Micronex™ (named the KDS MF-777) in Kunak, Malaysia. At present, only one-sixth of the EFB processed by the KDS MF-777 is necessary to supply TSH power plant. It processes 3750 kg/hr of raw EFB having a moisture content of 52% producing 3000 kg/hr of shredded EFB with a moisture content of 40%, which is dry enough for burning on a grate. The power consumption of the MF-777 is only 200 kW under these operating conditions. This translates to a drying energy consumption of only 960 kJ per kg of water removal (= 414 BTU/lb).
Every percentage point of moisture in the biofuel causes 0.5-1% reduction in the electricity produced. Thus, the maximum possible increase in the TSH power plant output because of drying the biofuel is 0.84-1.68MWe. Thus, a net overall increase in the total power generated becomes possible due to the KDS MF-777. Therefore, our customer recouped the cost of the KDS MF-777 from the extra revenue due to the increased electricity production.
Bagasse is the name of crushed sugarcane after removing the cane juice. The production of sugar in Louisiana (USA), Brazil, Indonesia, and India generates immense quantities of bagasse. Though it has 40% water content, sugar producers use it as boiler biofuel. However, burning bagasse in its wet state significantly lowers the efficiency of the steam boilers.
The KDS Micronex exhibits its best drying performance while processing wet fibrous substances. For example, alfalfa hay, bagasse, and deinking sludge. Tests have shown that the machine uses only 1500 kilojoules of energy to remove 1kg of water from bagasse. This is lower than the latent heat of water because the machine uses mechanical forces for dewatering.
Tests have shown that the machine can dry 0.75tph feed rate of bagasse from 44% water content down to 21%. In this case, its total power consumption is 120 kWh. The KDS Micronex is able to adjust the product particle size from coarse fibers to a fine powder. Much higher bagasse feed rates are possible with a more powerful grinding motor. Along with that, energy consumption per fed ton will become less, at higher feed rates.
Alfalfa hay, a similar fibrous material, needs only 75kWhr/ton grinding energy consumption. So, it will be much less than the gross increase in electric power production, when bagasse-fueled boilers. This will result in a net increase in the thermal efficiency which will help pay for the extra cost of the drying equipment.
Companies producing paper generate large quantities of deinking sludge. Common sludge management practices of land-filling and land-application are under environmental scrutiny and are becoming increasingly costly.
Benefits of using the KDS Micronex™
The KDS Micronex can dewater deinking sludge. In addition, it enables to separate paper fiber from other paper components (i.e. kaolin clay). The paper fiber can be recovered for fuel or recycled as fiber. Kaolin clay can be recycled in the papermaking process or other industrial applications. The removal of clay also significantly increases the biofuel value of and reduces the ash created during combustion. We designed turn-key solution using the KDS Micronex to recycle sludges from the pulp and paper industry.
Tests show that 900kg/hr feed rate of deinking sludge can be dried down from 38% moisture to 16%. The total power consumption, in this case, is only 90 kW and a water removal rate of 236 kg/hr. Thus, the specific power consumption is 100 kWhr for a metric ton of input material. This is 136 kWhr per ton of output product. The water removal energy was 381 kWhr/ton or 1373 kilojoules per kg of water removal., or 1.373 GJ/ton. The theoretical minimum energy for water removal (latent heat of water) equals about 2258 kilojoules per kg of water.
Conventional thermal dryers use up to 3800kilojoules of energy to remove 1kg of water, i.e., 3.8 GJ/ton. Thus, the KDS Micronex uses only 36% of the energy that a conventional dryer uses.
Cost advantage of using the KDS Micronex™
Assume that electric power costs $0.06/KWhr and natural gas (the cheapest of all conventional dryer fuels) costs $8 per gigajoule. The drying energy cost is 0.06 x 381 = $22.86 per ton of water removed in the KDS Micronex. In a conventional dryer, the cost would be 3.8 x 8 = 30.4 per ton of water removal.
Thus, the KDS Micronex has a 25% cost advantage over conventional dryers. It is under the assumption that the relative prices of electricity and natural gas stay the same.
Clay and fiber components of deinking sludge CANNOT be separated from the deinking sludge dried in a drum dryer. In contrast, the KDS Micronex produces a fluffy, fibrous product. This enables to separate the clay from the residual fiber. After that, a company can burn it in boilers as fuel. The clay can be calcined and reused in the paper-making process.
Similarly, extensive testing is done in Ontario, Canada with a local deinking sludge. It showed that the machine is able to process deinking sludge at similar feed rates and power consumption from an initial water content of 50% to a final water content of 15%, i.e., water removal rate of 370kg/hr with a total power consumption of 100 kW.
This represents even better economics than in the U.K testing, i.e., 33% cost advantage over a natural gas-fired dryer.
Wood waste which is unsuitable for timber or pulp can be a disposal problem for the forestry industry. Companies operating in the industry are able to burn wood waste efficiently as a renewable energy source. However wet wood is often only marginally economic because up to 40% of the heat value in the wood is necessary to dry the moisture in the wood chips.
The KDS Micronex is an alternative to traditional methods of drying wood as it combines both the pulverizing and drying operations in one compact machine, thereby simplifying the process. Furthermore, the machine can handle contaminants such as dirt and stones that can cause sparking and fires in hammer mills.
While grinding spruce/pine/fir (SPF) hog fuel of 25 mm/1in size and 14% water content, the KDS Micronex consumes 150 kW for every ton per hour, producing output with a median size of 600 microns (30 mesh) with a maximum of 2mm. With 50% moist SPF or hemlock wood chips, the energy consumption is 300 kWhr/ton. The machine removes 135 kg/hr of water when the grinding power consumption is 150 kW.
FASC has dried and ground wet sawdust from the initial moisture of 48% down to 15% while also making a fine powder out of it. 185 kg/hr of such fine powder having a median particle size of 250 microns was produced with a grinding power consumption of 140 kW. This fine, dry powder was then utilized to make a wood-plastic composite.
The KDS Micronex was chosen as the equipment of choice because no separate dryer or heat source was necessary. Hammer-mills are unsuitable for such fine grinding. Attrition mills can be used but they require the feedstock to be first pre-processed in a hammer mill and their capacity is limited.
A scientific paper by Holtzapple et al. reports that attrition mills have an energy requirement of 261 kWhr/ton (0.94 MJ/kg) to grind down to 850 microns and 656 kWhr/ton (2.36 MJ/kg) to grind down to 106 microns top size. This does not include the energy for drying the wood.
An economic analysis shows that in this particular case, the KDS Micronex and conventional technology are roughly comparable in terms of their energy cost. The KDS Micronex does have the advantage of requiring no heat input and combines the functions of both a conventional dryer and grinder.
A test in which the KDS Micronex dried and ground SPF bark showed that the machine is able to grind and dry 636 kg/hr of bark with 50% water content to produce 361 kg/hr of product with 12% final moisture content and a median particle diameter of 250 microns. The water removal rate was 277 kg/hr (twice that achievable with wood) and the total power consumption was 180 kW. Such fine grinding down to 250 microns median diameter is necessary if a dust burner will burn the bark powder.
At $0.06/kWhr electricity cost, the total grinding and drying energy cost in the KDS Micronex was $16.98 per metric ton. The conventional technology to dry and grind wet wood-bark is a drum dryer, hammer mill, and attrition mill combination. With $8/GJ dryer fuel cost and an energy consumption of 3.8 GJ per ton of water, the drying cost in a drum dryer would have been $8.42 per hour or $13.24 per metric ton of feed material.
The grinding cost would have been $6.5 per hour or $10.21 per feed ton, assuming 300 kWhr/ton grinding energy requirement in the hammer mill and attrition mill [Ref: Holtzapple et al.]. Thus, with conventional technology, the total drying and grinding cost would have been $23.45 per feed ton. Thus, the machine, in this case, has a 27% cost advantage over conventional technology.
Sewage sludge, also called digested sludge or “biosolids” are created at wastewater treatment plants as water is processed and purified. Currently, many municipalities are facing challenges to environmentally and economically dispose of wastewater treatment plant biosolids.
The KDS Micronex can dewater biosolids to reduce their volume and the associated transportation and disposal costs. The KDS Micronex is certified by the US Environmental Protection Agency for its ability to destroy pathogens including salmonella, e-coli, and fecal coliforms. The dry powders produced by the KDS Micronex are suitable for land application or for use as a fuel source where they can replace fossil fuels.
The results of extensive testing in British Columbia, Canada shows that the KDS Micronex is able to process sludge with 80% water at the rate of 300 kg/hr. As a result, the output product has only 10-13% water content. The machine can consistently reduce fecal coliform from over 4 million MPN/gram (Most Probable Number of fecal coliforms per gram) in the raw biosolids to well under 1000 MPN/gram in the output product.
This means that the product from the KDS Micronex met Class A standards for biosolids, which are much more valuable as fertilizer. The power consumption was 500 kWhr per metric ton of raw sludge. An economic analysis shows that the cost to process sludge is $80 per ton, including amortization, labor and power costs. This results in a production cost of $400 for one bone-dry ton of product.
According to a leading academic researcher, competing technologies that convert Class B to Class A biosolids have processing costs ranging from $400 to $800 per bone-dry ton. Thus, the economics of the KDS for this application are extremely competitive. While sludge-derived fertilizer is still rather expensive to produce, it is an environmental regulation that requires wastewater sludge be rendered pathogen-free. Hence, wastewater sludge beneficiation is one of the best applications for the KDS Micronex.
About half the electricity generated in the United States comes from coal-fired power plants. Large power plants dry and pulverize coal in a ball mill to under 75 microns (200 mesh) before burning. The drier the coal, the higher the value for burning. Coal moisture content can vary widely from 5 to 50%.
Testing by FASC indicates that the KDS Micronex is able to dry bituminous coal from 15% to 4% moisture content. It is also able to grind to a median diameter of 63 microns (230 mesh). The production rate, in this case, is 3-4 tons per hour. The grinding energy consumption of 30-40 kW hr/ton is competitive with that of small ball mills.
Unlike ball mills, the KDS Micronex machine reuses that grinding energy to dry the coal hence is actually more efficient. With the KDS Micronex, it is possible to increase the value of lower grade coals which have limited use at present.
The total volume of animal manure (cow, hog, chicken, and horse) in the United States is approximately 130 times greater than that of human waste. Animal manure has a long tradition of use as an effective fertilizer. However, with modern intensive agricultural production, manure volumes can exceed the capacity of nearby croplands to absorb the nutrients in the manure.
Media reports about numerous cases in which a violator inappropriately spreads manure contaminating both surface and groundwater. This negatively affects both human health and the environment.
The KDS Micronex can reduce animal manures to a fine dry powder. This powder is virtually free of both pathogens and offensive odors. In this dry state (approx. 10% moisture), the odor is significantly reduced. Customers are able to store, transport, and sell it as a fertilizer. It can also be blended, at the time of production, with a variety of other minerals and chemicals for the manufacture of custom fertilizers. Once processed it can be pelletized for easy application to farmlands.
The key advantages of the KDS Micronex are lower operating costs and small space requirements compared with conventional hammer mill and rotary drum dryer systems. The footprint of the machine is approximately 100 sq. feet which is about 1/5 the size of conventional systems. Conventional systems also require significantly more operating energy to dry manures compared to the KDS Micronex.
Dried manure and other biomass can also have a value as a fuel source. Micronex Systems Inc with its partners has developed complete turn-key solutions to cleanly and cost-effectively burn manure and generate “green” power.