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Can the air be cleaner when mills go cleaner?


July 1, 2007
By Pulp & Paper Canada

As described in last month’s issue, the opportunities around the biorefinery initiatives can lead to a whole range of new products which employ biomass as a feedstock in place of petroleum. While this…

As described in last month’s issue, the opportunities around the biorefinery initiatives can lead to a whole range of new products which employ biomass as a feedstock in place of petroleum. While this itself is exciting, from an environmental perspective there is tremendous potential that these suites of activities will lead to a reduction in the emission of air pollutants and hence prove beneficial for the air quality in communities where pulp and paper mills operate. Before further discussions we need to spend a bit of time examining the air pollutants that are presently on the radar screen of the Canadian public and the Canadian regulators.

Given the wealth of air time and information being devoted to the issue of global warming, it is not surprising that the suite of Green House Gases (GHGs) heads the list of substances of concern. The major greenhouse gases that are the subject of the Kyoto protocol are carbon dioxide, methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons and sulphur hexafluoride. Carbon dioxide is typically the reference greenhouse gas to which others are compared and has been given a Global Warming Potential (GWP) of 1. The GWP of the other greenhouse gases are provided in Table 1.

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As an example, a GWP of 21 for methane indicates that each tonne would have the same global warming potential, over the next 100 years, as 21 tonnes of carbon dioxide. Of the six GHGs, carbon dioxide, methane and nitrous oxide are the only ones relevant to the emissions from the pulp and paper industry. Another group of compounds that are of prime environmental interest falls into the category of Criteria Air Contaminants (CACs). These include total particulate matter, particulate matter with a diameter of <10 microns (PM10), particulate matter with a diameter <2.5 microns (PM2.5), sulphur dioxide (SO2), nitrogen oxides (NOx), volatile organic compounds (VOCs) and carbon monoxide (CO). Since these contaminants can be formed as by-products of combustion, they are all of direct relevance to the emissions from the pulp and paper industry. At present, CACs are tracked as part of the National Pollutant Release Inventory (NPRI), a Federal regulatory initiative that gathers information on over 300 pollutants released, disposed of, and recycled by companies and other organizations in Canada.

Reductions of GHGs and CACs are also a critical component of the Canadian Government’s “Clean Air Regulatory Agenda” released on April 26th, 2007 (see above reference). The agenda, referred to in advertising as Turning the Corner contains aggressive timelines and targets for the reduction of GHGs and CACs. In summary, for greenhouse gases, the framework sets a 2010 implementation date for emission intensity reduction targets. From a baseline year of 2006, the targets are to be a 6% reduction/year until 2010 followed by a 2% reduction/year up to 2020. For criteria air contaminants the framework is slightly more complicated and involves fixed National emission caps for NOx, SO2, VOCs and PM and sector-specific caps to be enforced as soon as possible between 2012-2015. These parameters will not be regulated equally for the various industrial sectors as there will be different targets and not all of the individual components will necessarily apply. At the time of this article’s writing, Environment Canada was actively holding consultation sessions with Industry and as such, additional details were not yet available.

This brings us back to the initial question: What are the opportunities for green initiatives and do they provide a beneficial impact on the emissions of contaminants released to the atmosphere? At present, for the pulp and paper sector, some of the larger green opportunities revolve around the use of gasification of bark and wood waste, anaerobic digestion of biosolids and carbon dioxide capture technologies. In order to examine the first green technology, we need to first define the term biomass gasification. Simply stated, biomass gasification is a means of converting the organic matter in bark or wood into a gaseous product called synthesis gas or “syngas” for short. This syngas is primarily composed of hydrogen and carbon monoxide in addition to lesser amounts of carbon dioxide, water, methane, complex carbohydrates and nitrogen. The key to gasification is that the reactions take place in an environment with minimal oxygen at a temperature of approximately 800-1000C. Due to the limited oxygen, only a portion of the fuel is burned completely and the heat generated helps to chemically breakdown the remaining bark or wood into the syngas. The syngas gas is then combusted in heat recovery equipment or directly fired in units such as boilers or kilns to produce heat, hot water, steam or electricity. While the principles of gasification are not by any means new or novel, recent advances in technology and the rising cost of fuel oil and natural gas have sparked new interest. This technique is now identified as an environmentally friendly option for the conversion of low cost solid wastes into renewable fuels for the pulp and paper industry.

Two-part key

The key to gasification technology’s “green” label is two-fold. First, the use of biomass is considered greenhouse gas neutral. The rationale for this is that plants absorb carbon dioxide as they grow and when they die this same carbon dioxide is returned to the atmosphere in a never-ending renewable cycle. Biomass is therefore considered greenhouse gas neutral since the amount of carbon dioxide emitted, as a result of combustion or gasification, is equal to what would be emitted if it were to decompose naturally. Secondly, the use of biomass gasification helps to displace the atmospheric emissions that would be associated with the burning of heavy fuel oils or natural gas. For example, a recent installation of Nexterra’s gasification technology at Tolko’s Heffley Creek plywood and veneer mill has led to a significant reduction in atmospheric emissions. The gasification plant has allowed the mill to displace 40% of its natural gas consumption resulting in a 12,000 tonne per year reduction in its greenhouse gas emissions. In addition, the gasification unit was designed to consume and eliminate the VOC emissions that are produced by one of the veneer dryers at the mill. Although more testing needs to be undertaken to fully evaluate the environmental benefits, Nexterra mentions that its biomass gasifier produces extremely low particulate emissions of <50 mg/m3. Since bark and wood have a low sulphur content and are in general a much cleaner burning fuel, the emissions of sulphur dioxide are also expected to be relatively low as compared to the use of fossil fuels. For example, using US EPA AP-42 emission factors, a moderate sized boiler burning residual fuel oil would emit approximately 15 times more sulphur dioxide and 10 times more particulate than a boiler operating with biomass. An additional environmental benefit could also be realized for some wood product facilities that currently dispose their bark and wood waste through the use of beehive burners. The switch to gasification units would enable these mills to shut down their beehive burners, resulting in a significant reduction in GHG and CAC emissions and an obvious improvement in air quality.

The second technology of interest is the potential for the anaerobic digestion of pulp and paper mill biosolids. The principle function of anaerobic digestion is to convert as much of the solids into biogas. Anaerobic digestion has been a proven technology for many years as a means of dealing with wastewater sludges from municipal sewage treatment plants. The process typically goes through several steps within a single or two-stage digester and can take greater than 20 days to achieve completion in the temperature range of 20-40C. The first step involves hydrolysis of the solids and conversion into simple sugars, amino acids and fatty acids. Further breakdown into volatile fatty acids, carbon dioxide, hydrogen and other smaller molecules then occurs. T
he final step in the process involves methanogenesis which produces methane, carbon dioxide and water. A typical system will produce 0.5-1 m3 of gas per kilogram of solids digested with a final gas composition of methane (65-70%) and carbon dioxide (25-30%) plus trace contaminants. The rationale for using anaerobic digestion to treat municipal wastewater treatment sludges is primarily to eliminate the pathogens and odours that are associated with this material, thereby increasing its potential for land spreading. While some of the gases may be combusted to provide heat for the process, energy production is not the primary goal for the municipalities and most will simply flare the excess methane produced.

Current situation

In Canada, there are approximately 70 pulp and paper mills that operate activated sludge treatment facilities which necessitate the handling and dewatering of tonnes of biosolids per day. Given a typical biosolids production of 50 kg/t of product, this transcends into a large potential source of green energy. However, despite hundreds of anaerobic sludge digestion installations in the municipal sector worldwide, to our knowledge there are no full-scale facilities currently operating within the pulp and paper industry likely due to the high capital requirements. Tembec operates an anaerobic treatment plant at its facilities in Temiscaming; however, it is treating a concentrated liquid effluent which is a much easier feedstock to handle. The high cost of anaerobic digestion for the pulp and paper sector is related to the relatively long digestion times which in turn require large capital investments for holding tanks.

Current research at FPInnovations-Paprican Division, is evaluating pre-conditioning technologies that can efficiently solubilize the biosolids allowing anaerobic digestion to be completed in as little as one week. Therefore, in the near future, anaerobic digestion may become a viable alternative for the production of green energy. What does this mean from an environmental point of view? As was the case with gasification, the methane generated from anaerobic digestion would be used to offset the current use of natural gas or fuel oil and would reap the same benefits as previously described. In addition, there would be a reduction in the amount of biosolids being put into landfills which would preserve landfill capacity for other wastes where diversion options are less viable. When biosolids are added to landfills, the organic wastes break down over a long period of time and in the process produce methane (~55%), carbon dioxide (~42%) and acid leachates which can contain hydrogen sulphide (high ppm levels) and cause the release of metals. Since methane is 21 times more powerful than carbon dioxide as a greenhouse gas, its uncontrolled release from landfills can contribute to global warming. When biosolids are treated by anaerobic digestion, all of the methane that is produced would be captured in an environmentally sound manner and, when combusted, be converted entirely to carbon dioxide. Anaerobic digestion of biosolids is a means of minimizing the global warming potential of this pulp mill source. An additional environmental benefit is related to the reduction in the volume of solids that need to be transported. Reduced volume leads to fewer loads translating into a reduction in the diesel emissions associated with transportation.

The third “green” initiative is the use of carbon dioxide capture technology. The environmental benefits of this technology are of course related to the removal of greenhouse gases from the atmosphere. One such system involved in evaluation by FPInnovations – Paprican Division has been is Cansolv Technologies (CTI) of Montreal. CTI’s process involves the use of an aqueous amine based solvent that can be used to absorb the carbon dioxide out of pulp and paper combustion stacks such as the lime kiln or power boiler. Once captured, the CO2-laden amine is pumped to a regeneration tower where it is heated in order to regenerate the amine and release high purity carbon dioxide. The carbon dioxide produced from this technology has various applications in the pulp and paper industry. Such applications include calcium carbonate production, lignin precipitation at kraft mills and various pH adjustment applications (i.e, bleached mechanical pulps prior to papermaking, whitewater and mill effluents). While this technology has not yet been implemented in the pulp and paper industry at full scale, the Federal Government’s new Clean Air initiatives and discussions around the issue of carbon credits and trading, may lead to additional interest in the future.

So in response to the question, “Can the Air be Cleaner When Mills Go Cleaner?” in certain cases, the answer is a resounding “Yes!”

Brian O’Connor is Program Manager, Environment at FPInnovations – Paprican Division.

Table 1: The Global Warming Potential of various greenhouse gases

Gas100 Year Global Warming Potential
Carbon dioxide1
Methane21
Nitrous oxide310
Hydrofluorocarbons140 – 11,700
Perfluorocarbons6,500 – 9,200
Sulphur hexafluoride23,900

Obtained from on-line Environment Canada document “Regulatory Framework for Air Emissions, http://www.ecoaction.gc.ca//news- nouvelles/20070426-1-eng.cfm”.

AL-PAC GOES NEUTRAL

Al-Pac now stands as the only pulp mill in North America to be carbon neutral. A number of initiatives culminated in the achievement of this milestone, yet they were all guided by the same principle: an effort to minimize environmental impacts.

The company’s manufacturing operations reduced direct mill greenhouse gas emissions from 187,236 tonnes of carbon dioxide equivalent (CO2e) in 1994 to 99,973 tonnes CO2e in 2006, a decrease of 47% since the first year of operation. During the same period, the company’s pulp production increased 33% to a 1,802 tonnes per day average. For each tonne of pulp produced, direct emissions declined from 0.40 tonnes CO2e in 1994 to 0.16 tonnes CO2e in 2006.

These direct emissions were offset by the carbon sequestered through the company’s poplar plantations and its programs to avoid industrial forest clearing.

“All of our team members’ contributions to our carbon neutrality status led to this achievement,” said Ken Plourde, director of Al-Pac’s forest strategies. “While our commitment to protecting the environment is central in everything we do, our efforts to reduce carbon also provide us with cost savings.”

Integral to reaching carbon neutrality was also the company’s electrical power self-sufficiency and ability to export excess power at peak times to the Alberta electric system. The company planted roughly 4,200 hectares of poplar plantations since 2001, and another 1,200 are planned for 2007. The company’s integrated land management program reduces the industrial footprint, road and truck design improvements, technological advancements and a reduction in truck haulage all contributed to Al-Pac’s carbon neutral status.


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