Written by Roxare on June 7th, 2009
With the increasing cost of energy and mounting environmental concerns about emissions, a few pulp mills are installing biomass gasifications as an alternative source of energy See here. One recent example is the Kruger tissue mill in New Westminster, BC. The mill is installing a gasification system to convert locally –sourced wood residue into syngas, which will be fired into a boiler, replacing natural gas. The system start-up is scheduled for December 2009, and will produce 40,000 lb/hr of process steam and replace around 445,000 GJ of natural gas per year [1]. The gasification process uses 20-30% of the oxygen required for complete combustion. Through pyrolysis, a syngas is produced which mainly consists of carbon monoxide, hydrogen and methane. The main advantage of syngas compared to hog fuel is that it is a clean fuel; hog fuel generates a significant amount of particulate emissions. It is estimated that New Westminster installation will save millions of dollars in energy costs.
Other related projects in the pipeline are an ethanol production plant in Westbury, Quebec that will produce ethanol from old utility poles, and a plant in Edmonton, Alberta, which will produce ethanol from municipal solid waste. These projects indicate another option for wood residues in the pulp and paper industry. Click to continue »
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Posted in Biorefinery, Energy | No Responses »
Written by Roxare on April 5th, 2009
New recovery boilers are being installed around the world which are bigger, have higher efficiencies and produce more electricity. Producing green electricity for sale based on renewable resources has put a new focus on the recovery operation. About 80% of the 20 most recent recovery installations have higher pressures (>85 bar) and higher temperatures (>480o C). New recovery boilers have capacities of more than 5000 tds/day, with some evaporation units exceeding 1000 t H2O/h water removal capacity [1].
New recovery capacity is being built in Asia and South America, where half of the new mills produce HW pulp (Eucalyptus). Europe and North America account for less than half of total new recovery capacity. In Europe and North America, there are a lot of old recovery boilers, with an average age of 30 years. Since the life expectancy of a recovery boiler is about 30-40 years, significant investment in older mills is required within the next 10 years. The alternative is mill closure. Click to continue »
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Posted in Recovery Boiler, Recovery Cycle | No Responses »
Written by Roxare on January 18th, 2009
The viscosity of black liquor affects its handling properties and is a critical parameter for the control of a recovery furnace, in terms of the spray characteristics and the char bed size and shape. Many mills have increased the as-fired black liquor solids in order to improve their boiler’s thermal efficiency, increase liquor throughput and reduce environmental emissions. However, black liquor viscosity increases significantly at solids concentrations over 70%. If a mill is not equipped with a pressurized liquor handling system, in which high temperatures can be used to reduce viscosity, another viscosity reduction method such as alkali profiling may have to be used to facilitate high solids firing. There are other methods to reduce viscosity, such as liquor heat treatment or high temperature oxidation, but these involve capital cost. For more information on black liquor viscosity see my posts of May 26, June 9 and June 28, 2007. Click to continue »
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Posted in Black liquor viscosity, Recovery Boiler | 2 Responses »
Written by Roxare on November 16th, 2008
Modern recovery boilers (RB) operating at high bed temperatures have, typically, a low SO2 emission. These RBs have a modern air system and, by firing liquor at high solids concentrations, create adequate burning intensity and mixing in the lower furnace. Older boilers operating at high sulfidity, low dry solids and/or a not sufficient air system will have a high SO2 emission rate, i.e., around 1000 mg/Nm3 [1].
The molar ratio of S/Na in black liquor (BL), along with furnace operating conditions, determine the chemistry of the S and Na in the flue gas. Based on the results obtained from a flue gas survey of different boilers, the range for Na and S emissions has been examined. For RBs with a low S/Na ratio in the flue gas (high burning intensity) and a hot bed, more Na is released than needed to bind with S, resulting in little or no SO2 emission. The fly ash will contain a high Na2CO3 concentration, corresponding to a high pH. RBs with a high S/Na ratio in the flue gas have low burning intensity and colder beds that do not release enough Na to capture S, resulting in more SO2 emission and the formation of acidic sulfates, which lower the sticky point of the ash and its pH. Click to continue »
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Posted in Recovery Boiler, SO2 emission | 2 Responses »
Written by Roxare on October 13th, 2008
I have covered this subject under different postings in the past [March and April 2007]. However, this is an up to date review with some new information regarding the nature of scaling in black liquor evaporators [1].
Sodium salt scaling takes place in black liquor [BL] evaporators, smelt dissolving tanks and green liquor lines. Scaling occurs when crystals nucleate from solution on pipe walls or heat transfer surfaces. In a solution containing no precipitated salt, nucleation occurs when the solution become supersaturated to the point where the metastable limit for the system is exceeded. The level of supersaturation depends on the solution, the process, the number of hetero-nuclei, the heating rate, the residence time and, sometimes, the shear rate [1]. Click to continue »
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Posted in Evaporator scaling, Sodium salts scaling | No Responses »
Written by Roxare on September 15th, 2008
Here is a summary of a recent article by J.D. McNutt [1] which I think is timely and interesting.
We all know that the pulp and paper manufacturing is an industry in difficulty. A new integrated, virgin fibre-based mill has not been built in North America (NA) in more than 17 years. Value creation and stocks have gone nowhere over the past decade, making new investments unlikely. However, in the past, some really bad industries have turned around with strong asset management discipline and consolidation; an example is the steel industry. The possibility exists for the pulp and paper industry to turn around, judging by investments made by some private equity firms. Private equity is paying about 30-40% of invested capital costs for assets. With a new focus on capital asset management, older assets (capacity) are being permanently retired, resulting in both lower capacities and improved asset quality. This constrained new capacity investment and focused asset management climate should help paper companies to reach healthier returns on invested capital. Click to continue »
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Posted in Value | No Responses »
Written by Roxare on July 27th, 2008
The main reason for applying nanotechnology solutions is added value. Nanotechnology in papermaking can be applied in several areas. These include:
- Water based coatings that are non-toxic, smoother and tougher
- Surfaces that are smoother and have better printability
- Enhanced sheet properties by adding nanoparticles such as silica
- Developing grades that are stronger and lighter, use less fibre and are biodegradable
- Closed looped water reuse with nano-filtration
In traditional paper making, nano-particle-based fillers, substituting for fibre, and combined with lower basis weights, are delivering significant savings to the industry. Also, wet end retention aids are another example of existing nanotechnology. Click to continue »
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Posted in Nanotechnology | No Responses »
Written by Roxare on June 14th, 2008
The Blue Ridge Paper Products (formerly Champion), Canton mill, NC, recycles both the Eop and D0 filtrates to meet strict permit requirements, for water use and effluent colour. As part of Champion International, the mill undertook an aggressive bleach filtrate recycle strategy (the BFR process). This strategy incorporates a metals removal process (MRP, i.e., based on ion-exchange technology) and a chloride/potassium removal process (CRP, i.e., based on evaporation-crystallization of ESP dust) into the recycling operation [1]. BFR uses oxygen delignification followed by three stages of post-oxygen washing and ECF medium consistency bleaching (OD0EopD), with recycle of bleach plant filtrate to the recovery system. To optimize bleach plant operation, the chlorine dioxide charge in the D0 stage was reduced from a kappa factor of 0.28 to between 0.18-0.22 before the recycle began [2]. Eop filtrate is recycled to the showers of the last post-oxygen washer, and D0 filtrate is processed through a metal removal process before being recycled to the D0 washer. A portion of the final D-stage filtrate is sewered, because of the minimal environmental effect and the higher chloride load that would have to be recovered. Click to continue »
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Posted in Closed Cycle, System Closure | No Responses »
Written by Roxare on May 11th, 2008
Trace element (TE) distributions for As, Cd, Cr, Mn, Ni and Pb have been studied around the recovery boiler of a softwood kraft mill [1].The fate of these elements is of interest in closed cycle mills, where their toxicity could be an issue. An extensive sampling program was conducted in the mill, which had a production rate of 1700 adt/d, and used TCF bleaching. The black liquor was fired at 80%, and the capacity of the recovery boiler (RB) was 3000 t BLS/d. The lime kiln had a capacity of 500 t CaO/d; the lime was dried from 80% to 100% dry solids before burning. About 2% of the CaO used in the causticizing was added as make-up lime. Click to continue »
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Posted in Recovery Cycle, Trace Elements | No Responses »
Written by Roxare on April 11th, 2008
Effluents from the woodroom, the brownstock area and the evaporation plant have the highest toxic emission factor per COD unit, compared to the effluent from ECF or TCF bleaching [1]. Steps taken to reuse these effluents lead to high levels of non-process elements (NPEs) in the liquor cycle. The levels of NPEs for five Swedish mills were monitored for 7 years, and the data were used to evaluate the effect of increased mill closure, and to identify suitable methods to purge NPEs. Click to continue »
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Posted in NPEs | No Responses »
