Progressive System Closure — Developments and Approaches
By Pulp & Paper Canada
By Pulp & Paper Canada
QUESTION 1. What are some of the advantages associated with closed-cycle operation?
QUESTION 1. What are some of the advantages associated with closed-cycle operation?
Ideally, the different technological options available to mills should be evaluated and optimized using a full life-cycle assessment (LCA). Before an LCA is conducted, a complete mass and energy balance is required. Through this holistic approach, it may be found, for example, that complete elimination of effluent is not necessarily the best alternative in all cases.
Closed-cycle operation could result in several benefits to a mill or the industry in general. These include: reduced resource utilization, improved customer satisfaction and community relations, freedom to site mills in areas without a ready source of water and protection from future costs to meet tightening effluent regulations. System closure is gaining support in Canada as a way to achieve further effluent reduction, conserve energy and minimize the costs of environmental protection.
Based on a recent Paprican survey of member company mills, in the last few years, significant reductions in water consumption have been achieved in all sectors of the Canadian pulp and paper industry. In the kraft pulp mill sector, we have seen increasingly more mills implement better water management practices, reuse of cooling water, conversion of fresh water showers to condensate or whitewater and closure of vacuum pump systems. In the mechanical pulp mill sector, several pulp mills implemented heat recovery as well as white water, seal and cooling water reuse. Improved water management was the most common strategy implemented for advancing water use reduction at paper and board mills. Water savings due to cooling, gland and vacuum pump seal water recirculation were also significant. Other water conservation measures used were in the areas of broke handling, stock dilution, lubrication and condensate handling.
QUESTION 2. What has been Paprican’s approach to system closure?
Since, in the foreseeable future, no greenfield mill installations are envisioned in Canada, the emphasis has been on developing system closure strategies and technologies that can be progressively incorporated into existing installations. Achieving system closure in such mills poses quite a different set of challenges and risks as compared to designing a new mill with system closure in mind. In the context of progressive system closure, the risks are minimized through the step-wise demonstration and implementation of the proposed technologies and strategies and a continuous process of project-success evaluation, modeling and validation to assure the mill’s objectives are met with respect to product quality, compliance with environmental regulations and economics. Our philosophy has generally been to develop system closure approaches that result in lower costs compared to present systems while maintaining or improving process efficiency and product quality. Based on these criteria, over the last ten years, we developed several approaches which would allow pulp and paper mills to achieve progressive system closure. We collectively refer to these approaches as Paprican’s Progressive System Closure (PPSC) suite of technologies and strategies. The PPSC suite currently includes a whole array of technologies and strategies in the areas of water use reduction, improved prediction and design tools, dynamics and control, corrosion control, chemical separation and regeneration, removal and/or control of wood extractives, chemical additives, energy cost reduction and control of solid and gaseous emissions. The PPSC technologies and strategies were developed with funding from member companies and Industry Canada through its Technology Partnership Canada (TPC) program. In addition, various allied companies contributed to the development and/or demonstration of particular technologies through strategic alliances. The PPSC approach builds on a strong foundation of fundamental science, uses technologies which are relatively simple to install and operate and strives to keep the overall capital costs involved in system installation low. The PPSC approach can be adapted to different starting mill configurations and as a result, improves the probability of successful implementation.
QUESTION 3. Which are some of the recent achievements of the progressive system closure program?
For kraft pulp mills, we have been addressing the technical issues arising from alkaline bleaching filtrate recycle to the second post-oxygen washer. These issues include: accumulation of excess chloride in the kraft recovery cycle, increased organics carryover to the bleach plant and accumulation of excess sodium hydroxide in the kraft recovery cycle. In addressing these issues we:
a) Successfully demonstrated the Precipitator Dust Purification (PDP) chloride removal system at a member company mill. High chloride levels in the kraft recovery cycle can lead to plugging of the recovery boiler flue gas passages and corrosion of equipment — these problems could translate to millions of dollars in lost pulp, steam and electricity production as well as equipment replacement. The PDP system was operated continuously over a period of eight months to remove sodium chloride from dissolved ESP dust (1 tonne/d) and to enable the recycle of the chloride-free sodium sulphate/carbonate product to the chemical recovery cycle. Over this time period, the resin bed of the PDP system consistently achieved a high sodium chloride removal efficiency (95%) and high sodium sulphate (97%) and sodium carbonate (97%) recoveries. Funding for this demonstration was provided by Environment Canada and NSERC. This system is presently being commercialized by Noram Engineering and Constructors of Vancouver, BC and, following the demonstration of this system, we have received requests for quotations from several mills around the globe.
b) Evaluated the impact of alkaline bleaching filtrate recycle on ClO2 demand in a D0EopD1E2D2 bleaching sequence using O2-delignified kraft softwood pulp from a member company mill. We used the Paprican Bleaching Sequencer, an automatic device which simulates the bleaching stages and washing configuration of industrial bleach plants. Based on the results obtained, we concluded that: 1) the pH of the first bleaching stage should be controlled to reduce the effect of alkaline bleaching filtrate recycle on pulp bleachability, 2) Eop kappa no. is not a good indicator of the final pulp brightness — consideration of all stages where ClO2 is applied will give a more accurate estimate of the increase in ClO2 consumption, and 3) most mills should be able to increase Eop filtrate organic loading to the bleach plant by as much as 10 kg/odt without any negative impact on pulp bleachability or chemical consumption.
c) expanded CADSIM Plus dynamic model of a member company mill to include the hot water system, cooling tower and some area heat exchangers. This model was used to assist the member company mill to plan and conduct alkaline bleaching filtrate recycle trials and to decide how much ESP dust needs to be treated for chloride control. So far, the mill has been able to recycle as much as 300 USgpm of alkaline bleaching filtrate to the second post-oxygen washer without any major problems with respect to increased bleaching chemical consumption or pulp quality.
For BCTMP mills, we successfully demonstrated the Green Liquor Splitter (GLS) system at a closed-cycle member company mill. The GLS system was operated continuously over a period of 165 days to remove sodium hydrosulphide from the green liquor (dissolved smelt), which allowed the use of the sulphide-free sodium carbonate/hydroxide product, as a source of alkali in bleaching. Over this time period, the resin bed of the GLS system consistently achieved high sodium hydrosulphide removal efficiency (97%) and high sodium carbonate (95%) and sodium hydroxide (86%) recoveries. By the end of the trial, we accumulated 320 m3 of sulphide-free sodium carbonate/hydroxide product, which enabled the mil
l to run two successful bleaching trials. This member company mill is expected to save as much as $6 million/y following the full implementation of the GLS system. NORAM Engineering and Constructors of Vancouver, BC are currently commercializing the GLS system.
For sulphite mills, we developed several approaches for the purification of weak acid condensate which could then be returned to the fibreline as wash water. In a trial at a member company mill, we successfully demonstrated the complete destruction of sulphur dioxide and other odorous compounds in this stream, thereby providing the mill with the opportunity to offload their effluent treatment system (the production bottleneck) by about 10% with respect to BOD while achieving significant savings in effluent neutralization and treatment — we estimated that this particular mill could achieve savings of $2.5 million/y in incremental pulp production or $0.6 million/y in savings associated with the operation of the effluent treatment system.
We have also evaluated at the pilot plant scale, in collaboration with Cansolv Technologies Inc. (CTI) of Montreal, CTI’s amine-based carbon dioxide capture technology. The CTI system was operated continuously over a period of 610 hours treating flue gas from one of Paprican’s natural gas-fired boilers. Over this time period, we established the technical feasibility and economic viability of this process by investigating the rate of amine degradation, regeneration of the amine to remove heat-stable salts using an ion-exchange process developed here. We also evaluated the quality of the product CO2 which was found by independent laboratory tests to be food-grade quality. We expect this technology to be used in various applications in the pulp and paper industry including: PCC production at mills without a lime kiln, lignin precipitation at kraft mills for offloading their recovery boilers and various pH adjustment applications (e.g. of peroxide-bleached mechanical pulps prior to papermaking, whitewater and mill effluent). Funding for this demonstration was provided by NSERC-IRAP. This system is currently being implemented in the oil industry.
QUESTION 4. Are there ways by which we could expedite the implementation of system closure technologies in Canada?
Based on our experience, to be able to expedite the implementation of system closure technologies it is important to demonstrate these technologies on a small scale at a mill quickly following their development at the laboratory and/or pilot plant stage. As mentioned previously, in the case of two of our technologies, we were fortunate to receive funding from Environment Canada, NSERC and NSERC-IRAP. Another very important stage of development is the first full mill installation. In today’s economic climate, very few mills, mill engineers and/or managers are willing to take the risk of being the first; they would rather be the fifth or sixth to implement a new technology. It is my opinion that it would be in the interest of all stakeholders involved (mills, supplier companies, engineering companies, and provincial and federal governments) to share the risk associated with the first installation of any given technology. Even though the Federal Government has some great programs to promote sustainable development technologies, the rules relating to system commercialization and amortization should be sufficiently improved to allow struggling pulp and paper companies to be more receptive to the implementation of new system closure technologies and strategies. As shown by Pyry, a well-respected Finnish engineering and consulting company which was commissioned by Tembec to conduct a technical and economic evaluation of our system closure technologies, widespread adoption of the PPSC suite of technologies is expected to greatly improve the sustainability and competitiveness of the Canadian kraft pulp industry, and to position the associated technologies as a major export product. The drivers to adopt the technology in the industry include ever-tightening environmental legislation, and an imperative to keep the Canadian pulp industry competitive in the face of the modern world-scale mills that have been built in South America and Asia.
QUESTION 5. Looking into the future, how do you see the Canadian pulp and paper industry evolving with respect to further advancing system closure?
As a result of the sharp increase in energy prices over the last few years, the main driver for advancing system closure at Canadian mills has been energy cost reduction. It is widely understood that energy efficiency and fresh water consumption are closely linked. This is simply because every cubic metre of water discharged represents a certain amount of purchased energy in the form of waste heat. Therefore, any incremental reduction in fresh water use could lead to energy savings as well. System tools such as pinch analysis, in combination with a computerized heat and mass balance, have been used by Paprican staff to optimize the heat exchanger network of several member company mills. In 1999, a monograph published by Paprican and written in collaboration with several supplier companies provided a practical, action-oriented guide to energy cost reduction in the pulp and paper industry and has since assisted the industry in identifying and implementing several cost-effective projects in this area. More recently, data was collected from 49 mills relating to energy consumption at the mill level, as well as individual process areas. The variations in energy consumption for each process area indicated the realistic energy potential for energy reductions, thus enabling mill staff to identify where their operations are least efficient and to identify areas requiring changes in operating procedures or capital investments.
As we move into the future, in addition to energy cost reduction, another driver for advancing system closure will be the widespread realization that for North American mills to survive and remain competitive, they must diversify their product portfolio to include value-added products such as: functionalized fibres, transportation fuels (e.g. ethanol and biodiesel), polymers, food additives, neutraceuticals and pharmaceuticals — products currently produced from crude oil at petrochemical refineries. This is commonly referred to as the forest biorefinery concept. The successful realization of this concept will require: a) minimizing the loss of fibre, water, energy, organic and inorganic materials to the sewer, landfill or to the atmosphere, b) maximizing the recovery of all waste products prior to treatment and/or disposal and c) integrating several new and transformative process technologies and even industries into pulp mill operations while minimizing their environmental footprint and the loss of resources.
Michael Paleologou is Group Leader, Chemical Pulping at Paprican.