Fueling self sufficiency: pathways to change: black liquor and biomass gasification/ combined cycle is key to energy self-sufficiency in the pulp and paper industry. New research is needed to resolve several critical issues.

Editor's Note: This is port one of a two-part article on the use of self generated fuels for power generation in the pulp and paper industry. These articles are part of a continuing series of reports from the Forest, Wood and Paper Indus try Technology Summit, held in May 2001 in Peachtree City, Georgia, USA. The Technology Summit ways sponsored by TAPPI, AF&PA and the US Department of Energy's Office of Industrial Technology.

For more information, click on www.toppi.org/ctosummit.asp.

Our industry's vision is that integrated paper manufacturing will one day require no fossil fuel energy and even be a net exporter of electricity. Black liquor and biomass gasification combined-cycle is a key element in achieving this vision. It otters the potential to more than double electricity generation from captive self generated fuels.

Gasification converts low-cost solids (such as biomass) or liquids (such as black liquor) into clean-burning gases, usually for replacement of fossil fuels. Combined cycle denotes the use of a gaseous fuel in a gas turbine followed by the production of steam, which is then used in a steam turbine so that both turbines produce electric power. Figure 1 (page 68) compares the conventional model of power generation and consumption with this vision of the future.

[FIGURE 1 OMITTED]

SUMMIT MEETING

Driving this vision into reality was on the minds of industry experts gathered in Peachtree City, Georgia, for the industry's first Technology Summit in May 2001.

Their mission was to lay out the research path for the industry to pursue under the Agenda 2020 program to deliver commercially viable systems by 2008. The industry must develop these technologies promptly so they may be considered in capital planning as mills renew their steam generation equipment. Otherwise, our industry will miss a strategic opportunity to move toward self-sufficiency and other crosscutting advantages. Mills replace capital-intensive equipment such as steam generation units only after many years of service. The recent energy crisis has reminded everyone of how painful the lack of energy self-sufficiency can be.

Two days of working through the issues convinced the group that there is light at the end of the tunnel for gasification combined cycle in the paper industry. There are a few bumps and dips to cross, but the technology is poised to reach commercial success. To help in the final drive, the group identified the most critical technology/knowledge gaps and developed a set of recommendations to close those gaps through the Agenda 2020 Program.

The group identified two basic lines of black liquor gasification (BLG) development: low temperature (represented by MTCI's Steam Reformer) and high temperature (represented by Chemrec). The temperature distinction defines whether the technology operates below or above the melting point of the smelt produced. Both lines of development are poised for commercial demonstration, but some critical issues require resolution. Likewise, biomass gasification/combined-cycle (represented by the Battelle/FERCO process, among others) is ready for commercialization. (Editor's note: There are other processes for each line, but they are not being actively developed beyond lab-scale. For this reason, specific comments are made only for the MTCI, Chemrec, and Battelle/FERCO processes. Other processes are likely to encounter similar issues.)

A potential crosscutting advantage of BLG within the industry is the ability to damage the nature and form of chemical recovery to influence the chemical pulping process. This may lead to breakthroughs in fiber yield that would be unattainable with conventional recovery technology. Biomass gasification/combined cycle (BGCC) has crosscutting application lot other energy-intensive industries, such as chemicals, utilities, and refining.

A BRIEF HISTORY

In the mid-1970s, the global pulp and paper industry began to realize that the energy conversion equipment of that time was inefficient, capital intensive, and had safety and environmental issues. Both the Gunnar Sundblad Conference in Stockholm, Sweden, and the Forum on Kraft Recovery Alternatives in Appleton, Wisconsin, addressed this issue in 1976. At these conferences, researchers proposed several new technology options for kraft recovery. Twenty-five years later, the industry is ready for first demonstrations.

Since the 1930s, the Tomlinson recovery boiler has been the dominant technology for the recovery of chemicals and energy from spent pulping liquor (black liquor) of the kraft pulping process. There have been many attempts to develop alternatives, but none have achieved commercial success. While the Tomlinson furnace has enjoyed many improvements since its introduction, it still has relatively low thermal efficiency and a low power-output to total-heat-input ratio.

As recently as 1970, mills ascribed little value to hog fuel (wood room waste), and regarded it as more of a nuisance than a fuel. Many mills preferred to landfill it rather than reduce boiler capacity by displacing then-cheap oil. Higher fossil fuel prices focused more attention on the value of hog fuel; today, mills commonly burn it in a boiler designed specifically for such wastes or in a combination boiler burning fossil fuels as well. Hog fuel or combination boilers have drawbacks similar to recovery boilers, especially in that the power-output-to-total-heat-input ratio is low.

The industry can be proud of the progress it has made in using self-generated fuels, in spite of their poor characteristics. In 1972, these fuels supplied about 36% of the industry's steam and power needs. Through conservation efforts and improvements in combustion and power generation efficiencies, these materials now supply about 54% of steam and power needs for the pulp, paper, and packaging sector.

Never without challenges, our industry has continued to upgrade equipment used for pulping, papermaking, and forest products to increase productivity, achieve greater efficiency in fiber use and improve the quality of its products. Industry customers have become far more demanding about quality, particularly as their own technologies have become much more advanced. The cumulative effect of these changes has been to shift the amount of steam and power needed per unit of production to less steam but far more power. A modern paper machine has an electric power load per ton one-and-a-half to two times that of an older machine.

There have been pilot demonstrations of each of the two BIG technology lines. Low-temperature BLG was demonstrated in an MTCI Steam Reformer at Weyerhaeuser's facility in New Bern, North Carolina. High-temperature BLG at atmospheric pressure is commercially demonstrated in Chemrec units at Assi Domain-Frovifors, Sweden and Weyerhaeuser-New Bern. The pressurized design, suitable for combined-cycle, was demonstrated in a Chemrec unit at Stora-Skoghall, Sweden. Biomass gasification (BG) is being demonstrated in a Battelle-FERCO unit at Burlington, Vermont. As in most development programs, these demonstrations have led to much progress; however, significant questions remain In the case of BLG, demonstration projects slated for Georgia-Pacific in Big island, Virginia (an MTCI unit on soda process liquor), and Pitea, Sweden (a pressurized Chemrec design verification unit), may answer some of these questions.

GOALS AND GAPS

To be clear, the goal is not gasification The goal is to develop technology that achieves a step change increase in power generation from self-generated fuels and to make this technology available for consideration as the industry decides on equipment replacements and rebuilds. Gasification facilitates this by making it possible to couple combustion of these captive fuels with combustion turbines.

With this goal in mind, the group focused on making low-temperature (LT) and high-temperature (HT) BLGCC and BGCC commercial available and economically viable by 2008. The group identified each of the following gaps, and the research/technology development items intended to fill them, in that context. The author has organized the gaps by technology pathway, and by their status "critical" or "important." The industry must address critical items now support the overall timeline.

Gap Area 1 Gaps for LTBLG and HTBLG with potentially common solutions

Critical

* The need to define how pulping integration would make the economics even more compelling.

* The need to reduce the cost penalties associated with sulfur capture equipment.

Gap Area 2 Gaps for LTBLGCC

Critical

* What operating conditions or process enhancements will provide acceptable carbon conversion on kraft liquors without bed agglomeration?

* There are significant uncertainties created by the geometry of the commercial-size MTCI Steam Reformer unit.

* Is there a cost-effective way to offset or eliminate the highly increased causticizing cost under LTBLG conditions?

Important

* Will shield tubes materials of construction be a significant issue at the 1900[degrees]F expected the combustor tubes in MTCI Steam Reformer design?

* What can we do to control agglomeration in the fluidized bed? How much will liquor spraying design influence this?

* The need to understand the overall cycle efficiency/economics for the LTBLG designs with product gas compression. Should a pressurized design be developed?

* Complete design and economics for the gas cleanup systems suitable for combustion turbine quality product gas.

* Will tars be a serious issue under LTBLG conditions'?

Gap Area 3 Gaps for HTBLGCC

Critical

* A reactor lining material suit able for effective long-term operation.

* Is there a cost-effective way offset or eliminate the increased causticizing cost under HTBLG conditions?

Important

* The need to define green liquor system materials of construction for the 200[degrees]C conditions in the pressurized design.

* How can burner design be optimized for best efficiency and reliability?

* Will tars and trace species management be an issue under HTBLG conditions?

Gap Area 4 Gap for biomass GCC 

Critical

* How can tars be successfully managed?

Important

* How can nitrogen emissions be economically managed?

* Control system designs need to be developed.

* Are the economics sufficiently compelling? What is the sensitivity to power/biomass cost?

* Would integration of steam drying and indirect gasification systems make the economics significantly more compelling?

The group focused primarily on the eight "critical" issues in the four gap areas outlined above. The remainder of this article details the two critical gaps, and the proposed gap-filling programs, for the first area.

FILLING THE GAPS FOR LTBLG AND HTBLG

For BLGCC to become widely commercial, its economic case must be strengthened. Current projections place the capital cost of LT- and HTBLGCC higher than for conventional technology. The overall economics are favorable but not compelling when we consider only the benefit of increased power generation. This greatly shortchanges the potential value of BLGCC, since it may facilitate pulping chemistry breakthroughs in fiber yield that mills cannot economically attain with conventional recovery technology. However, this potential is largely unexplored and undeveloped.

First critical gap: The first gap-filling applied research needed is to assess the value and feasibility of integrating BIG with pulping for pulp yield improvement. For three concepts--polysulfide, split sulfidity, and alkaline sulfite anthraquinone (ASAQ)/minisulfide sulfite anthraquinone (MSSAQ) we must develop mass and energy balances and conduct laboratory cooks with simulated liquors to examine yield and end-use properties. For the ASAQ/MSSAQ process, researchers should assess materials of construction issues (especially regarding use of existing digester equipment), develop strategies for sulfite process scale-up (including demonstration trials), and conduct a literature review for sulfite pulping experience relevant to the kraft variant.

Conventional chemical recovery with the Tomlinson furnace principally recovers the cooking chemicals as sodium carbonate and sodium sulfide consistent with the proportions in the digester, since all the inorganics end up in the same molten smelt phase. In BLG, much of the sulfur ends up in the gas phase, while fine sodium ends up in the solid or molten smelt phase (prior to quenching). This provides the opportunity to create sulfur-lean/sulfur-rich cooking liquors. A number of variants to the kraft process can result in higher pulp yield:

* Polysulfide/enhanced polysulfide potentially offering a ~4% bleached pulp yield increase with the ~4% polysulfide concentration allowed by BLG.

* Split sulfidity offers a 1%-2% pulp yield increase.

* ASAQ and MSSAQ could result in an 8% yield increase on linerboard pulp and a 4% yield improvement with bleached pulp.

Researchers can demonstrate the most promising processes by using short-term trials on batch units and simulated cooking liquors. The first kraft demonstration projects tar LT- and HTBLG should include the most suitable process, based on the host mill's process and products.

The researchers to perform this work should have experience with some or all of the kraft variants to be explored. North Carolina State University (Hasan Jameel), PAPRICAN, and STFI have the requisite experience. Since scale-up is an important issue, a digester equipment supplier, such as Kvaerner or Andritz-Ahlstrom, should be involved in the program.

Second critical gap: The second gap-filling applied research need is to explore the economic feasibility of using calcium oxide/magnesium oxide (CaO/MgO) for hydrogen sulfide ([H.sub.2]S) capture from BLG product gas. A significant component of capital and operating costs for BLGCC is the use of sulfur capture processes. Researchers can use the following plan to assess the viability of this technology:

1. Measure [H.sub.2]S removal efficiency in laboratory scale experiments with simulated gas.

2. Assess regeneration and recycle efficiency.

3. Develop a preliminary design for the absorber,

The idea of using CaO/MgO for hydrogen sulfide capture has been experimentally demonstrated in proposals by Verrill and van Heinengen. The idea in BLG is that sulfur in the product gas would combine with solid calcium mid magnesium to form calcium sulfide (CaS) and magnesium sulfide (MgS). In concept, this process avoids the detrimental co-absorption of carbon dioxide (C[O.sub.2]), seen in conventional [H.sub.2]S recovery systems, and may reduce the equipment complexity. The sulfur is recovered by addition of caustic liquor, precipitating calcium hydroxide and magnesium hydroxide [Ca[(OH).sub.2]/Mg[(OH).sub.2]] that can be taken into the lime cycle.

The conventional approach to sulfur capture is amine-based absorption. These are commercially proven in the petrochemical industry although under conditions without entrained solid particles. They offer acceptable [H.sub.2]S removal selectivity versus C[O.sub.2], but add considerable complexity and capital cost.

If the technology appears very promising, it should be demonstrated on a slip-stream on LTBLG and HTBLC gasifiers (such as MTCI's pilot and the Chemrec atmospheric unit at New Bern or the pressurized unit at Pile& Sweden). The group suggests that this work should include the University of Maine (Adrian van Heinengen). Other potential participants suggested include US Filter or Marselex (for fluid bed absorber expertise), Chalmers University (Kristiina Iisa), and the University of Toronto.

Session Membership:

PAUL TUCKER (Session Leader)

KERRY BOWERS, Southern Company

ANDREW JONES, International Paper

JAMES FREDERICK, Chalmers University

KARL MORENCY, Georgia Pacific

RALPH OVEREND, National Renewable Energy Lab

KEVIN WHITTY, University of Utah 

Also contributing:

ADRIAN VAN HEINENGEN, University of Maine

HASAN JAMEEL, North Carolina state University

Editor's Note: Part 2 of this article will be published in the February 2002 issue of Solutions; It will explore the technology gaps unique to the three remaining areas: LT-BLGCC, HT-BLGCC, and biomass GCC Part 2 also covers the timeline for commercialization.

About the author. Paul Tucker is manager, energy and chemical recovery solutions for International Paper Co., Loveland, Ohio, USA He currently serves as a co-chair of AF&PA's Agenda 2020 Energy Performance Task Group. Contact him by email at [e-mail]