Mill residue

Adsorption. Adsorption (qv) is an effective means of lowering the concentration of dissolved organics in effluent. Activated carbon is the most widely used and effective adsorbent for dyes (4) and, it has been extensively studied in the waste treatment of the different classes of dyes, ie, acid, direct, basic, reactive, disperse, etc (5—22). Commercial activated carbon can be prepared from lignite and bituminous coal, wood, pulp mill residue, coconut shell, and blood and have a surface area ranging from 500—1400 m /g (23). The feasibiUty of adsorption on carbon for the removal of dissolved organic pollutants has been demonstrated by adsorption isotherms (24) (see Carbon, activated carbon). Several pilot-plant and commercial-scale systems using activated carbon adsorption columns have been developed (25—27). 

In the United States about 3 percent of all electricity produced comes from renewable sources of this a little more than half comes from biomass. Most biomass energy generation comes from the lumber and paper industries from their conversion of mill residues to in-house energy. Municipal solid waste also is an important fuel for electricity production approximately 16 percent ot all municipal solid waste is disposed of by combustion. Converting industrial and municipal waste into bioenergy also decreases the necessity for landfdl space. 

MILL RESIDUE RAIL Electricity ELECTRICITY ELECTRICITY... 

Any real application of pipeline transport of biomass from a field location (as opposed to mill residue) will normally require an initial truck haul to get the biomass to the pipeline inlet. This means that the fixed costs associated with both truck and pipeline transport are incurred. Thus, e.g., truck hauling of 2 million dry t/yr of biomass to a pipeline inlet at an average haul distance of 35 km (1), as might occur in a whole-forest harvest operation, with further transport of biomass by one- or two-way pipeline would have cost curves as shown in Fig. 3. The alternative of transport by truck alone is shown by the dashed line in Fig. 3. 

Raw materials for fiberboard manufacture come from several sources including whole wood, sawdust and mill residues, waste paper, agricultural wastes, and plant tissue other than woody stems. Additives usually enable attaining the desired properties but whole wood reduced to virgin fiberboard pulp often can be converted to board of impressive properties with little or no additives. High lignin content of virgin fiberboard pulps is usually cited as the source of this superiority. 

Up until 1952, all references found on bark in composition board were based upon wet-process softboard or hardboard. The first mention of a dry process came in a one-page article published by the British Columbia Research Council (30). The brief report indicated a dry process had been developed for making an interior wallboard possessing good strength and moisture resistance. No binder was necessary for the cedar mill residues, which included bark. Apparently, the process never was tried commercially. 

Solid wastes represent the ultimate in mill residues and include the accumulated refuse of the mill and the sludges from primary and secondary effluent treatment. There is difficulty in removing water from the secondary sludge the primary and secondary sludges often are mixed to aid in water removal, which is important if the sludge is to be incinerated for disposal. The sludges from pulp and paper mills are handled mostly as landfill, and sometimes, if not toxic, they are spread for agricultural purposes. 

Most wood and wood-derived materials (spent pulping liquors) that are used for energy are consumed by the forest products industry itself. The source of this fuel is almost entirely in the wood-processing and manufacturing operations, termed manufacturing residuals or mill residues. Forest residues from logging operations and the noncommercial trees in the forest also are utilized for fuels. 

The mixed wood and bark residues burned directly are collectively termed hog fuel. Over the past decade, there has been a trend to channel more and more of the cleaner, drier, and larger-sized mill residues into raw materials for products. The coarse wood residues (slabs, trim, edgings, etc.) are chipped and sent to pulp mills. Also, considerable sawdust now is being pulped instead of being burned for fuel. Some of the residues, including shavings, also are used for particleboard. This means that hog fuel contains the less desirable, dirtier, and wetter forms of waste. 

In another inventory of various sources of wood wastes in the United States (McKeever, 1995), it was found that for 1991, 26.0 million dry tonnes of bark and 74.5 million dry tonnes of wood residues were generated at primary lumber processing mills. Only 5% of the bark and 6% of the wood residue were wasted and not used. The projection for 1993 based on these findings was that 5.7 million dry tonnes of bark and wood residues were available for recovery and use as an energy resource. The total of 100.5 million dry t/year generated at the mills is about 44% higher than the mill residues found in the Stanford assessment. 

Assuming the results of the Stanford assessment of logging slash residues in the continental United States would provide approximately the same results today, the energy potential of 35.4 million dry t/year of slash is about 0.66 EJ/year unadjusted for availability. Similarly, 100.5 million dry t/year of mill residue is about 1.86 EJ/year. 

Howlett, K., and Gamache, A. (1977). Forest and Mill Residues as Potential Sources of Biomass, Vol, VI, Final Report, MTR 7347. The MITRE Corporation, McLean, VA. 

North Carolina Wood harvesting and pulp mill residues (black liquor)... 

Pulp and paper mill sludge is a complex and changeable mixture of dozens or even hundreds of compounds. Some are well known, like natural wood extractives, organochlorines, organosulfides, and dioxins. Priority pollutants and chemicals of concern that must be analyzed in pulp mill residues include heavy metals, chlorinated hydrocarbons, chlorobenzenes, PAHs, chlorinated phenols, chlorinated catechols, chlorinated guaiacols, phthalates, resin acids, alkylphenols and alkylphenol ethoxylates, and plant sterols. 

The Dakota Pellet Company makes fuel pellets from flax shives (8), which are sold to the city of Water-town, South Dakota and several local industries for 40 to 50/Ton. As a low cost pulp mill residue, the shives and dust from decorticated flax are a preprocessed residue. 

Ash picked up in loggirfg and storage can amount to 1C to 18% of mill residue bark. 

The minimum cost of feed pellets of seed cleanings is 40/T or 2.67/MBTU. Fuel pellets of bark are selling for 38/T delivered, 2.24/MBTU the sale price is close to our cost shown above. Direct cost of gathering and bringing field and forest residues to some point where they can be processed is between 1.50 and 2.40/MBTU. It appears that we must concentrate on the lower cost mill residues and wait for market changes to stimulate collection and densification of field and forest residues for industry. 

Wood now supplies about two percent of total U.S. energy needs, primarily through the use of manufacturing wastes and mill residues for boiler fuel. 

Forest residue is defined as the biomass left in the woods after harvest and includes tree tops, limbs, cull material, and all present and future non-merchantable trees. This differs from mill residue such as bark, edgings, and sawdust, which is often fully utilized as boiler fuel. The amount of residue remaining after harvest will vary according to merchantability standards, method of harvest, and forest stand composition and quality. In a typical hardwood sawlog harvest as much as 50 percent of the potential usable biomass may be left as residue. If the sawlog stand is overmature or of poor quality, additional residue may be left. In contrast, if the stand is whole-tree chipped for pulp material, very little residue will remain. 

As a byproduct of wood processing, extensive residuals are produced. Slabs, the rounded shell outside the sawn boards, always constituted a high proportion of the log, but the trend to shorter, economic rather than biologic rotations forced harvest of smaller trees, and increased the proportion of slab to board. These residuals are already salvaged by large mills. They are chipped and sold for pulping or used to supply heat and energy for mill operation. On a local scale, use of mill residuals may have a major impact. 

Due to the relative sparsity of timber inventory data it is difficult to accurately determine the total amount of wood residue available in the United States. However, estimates indicate that approximately three percent of the total United States energy demand could possibly be supplied by wood residues (2). There are several sources of wood residues suitable for fuel. A primary criteria is that the material be of a non-commercial nature and have a longterm and reliable supply. The primary sources of wood residue are forest and mill residue. The U.S. Forest Service publishes statistics which can provide the basis for estimating the potential amounts of available wood residues. Other state and regional organizations also publish data which are useful in estimating the quantity of available material(3). 

Mill residue is a source of wood waste which can be derived from the wood products industry. Depending on the efficiency of a mill, up to fifty percent of the incoming material can become waste material in the form of bark, sawdust, cut slabs, etc. (4). This residue is an excellent source of fuel however, for a long-term supply, it may dwindle as more emphasis is placed on utilizing it for "in-house" energy uses by the wood products industries. 

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