Changing the balance of power: black liquor and biomass gasification/ combined cycle are very promising technologies, but key research gaps must be filled prior to commercialization.

Editor's Note: This is part two of a two-part article by Paul Tucker of International Paper Co. 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 Industry Technology Summit, held in May 2001 in Peachtree City, Georgia, USA. The technology Summit was sponsored by TAPPI, AF&PA and the U.S. Department of Energy's Office of Industrial Technology. For more information, click on www.tappi.org/ctosummit.asp.

Our industry's vision is that integrated paper manufacturing will ultimately require no fossil fuel energy and even be a net exporter of electricity. As explained in last month's article, black liquor and biomass gasification combined-cycle is a key element in achieving this vision (see solutions!, January 2002, p. 67). At the Technology Summit, a group of pulp and paper industry energy experts gathered to mark the path for research to be pursued under the Agenda 2020 program to deliver commercially viable gasification/combined cycle systems by 2008.

There are two basic lines of black liquor gasification (BLG) development: low temperature, represented by the Steam Reformer (See Figure 1) from Manufacturing and Technology Conversion International Inc. (MTCI), and high temperature, represented by Chemrec's unit (See Figure 3). 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 (See Figure 5). 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.

[FIGURES 1-5 OMITTED]

The first part of this article identified the technology gaps for four separate areas: gaps common to low temperature and high temperature black liquor gasification (LT- and HT-BLG); and those specific to each of the three process streams--LTBLG Combined Cycle (CC), HTBLGCC, and biomass gasification combined cycle (BGCC.) Part 1 described those gaps as either critical (requiring immediate attention) or important and addressed in detail the actions needed to bridge the critical technology gaps for the first area. In this article, we will address the critical gaps in the three remaining areas. We will also review the timelines to support commercialization by 2008.

LOW-TEMPERATURE BLGCC GAPS The group identified three gaps unique for LT-BLGCC and critical to its commercialization.

Gap No.1: The first critical gap is that we do not know if carbon conversion in LT-BLG conditions can be made acceptably high in kraft-liquor applications. We must clear this obstacle for LT-BLG to become a major realized process breakthrough. Similarly, we lack a satisfactory understanding of the fate of sulfur for LT-BLG.

During its limited operating time, the MTCI pilot demonstration unit at the Weyerhaeuser facility in New Bern, North Carolina, USA, was not able to achieve carbon conversion adequate for a commercial unit (>97%). Experts have long viewed carbon conversion as the key technical challenge for LT:BLG because the melting temperature for kraft-liquor smelt creates an upper limit on operating temperature. The commercial demonstration unit at Georgia-Pacific's mill in Big Island, Virginia, LISA will process soda liquor; soda liquor produces a smelt with much higher melting temperature, creating a wide temperature operating window.

The first gap-filling research needed for LT-BLG is to confirm that we can effectively apply it to kraft liquors and determine the likely operating window. Lab- and pilot-scale experiments will be conducted to develop a fundamental understanding of carbon conversion/sulfate reduction kinetics under LTBLG conditions. This is a critical technology development step in making the broadest application of LT-BLG. The work should:

* Conduct collaborative pilot plant experiments with kraft liquor to evaluate carbon conversion, sulfur reduction and bed stability.

* On lab scale, develop kinetic models (with mechanisms) for kraft and carbonate liquors, evaluated under conditions of indirect heating and direct steam fluidization (the MTCI Steam Reforming process). We must identify the optimum conditions for carbon conversion, which is critical to success on kraft liquors.

* Determine the fate of sulfur and chloride. We need to understand how the sulfur partitions (gas vs. solid phase) and in what form. Understanding the sulfate-to-sulfide ratio is critical for making application to kraft liquors since sulfate represents "dead load." Chloride affects the agglomeration temperature, so we need to understand how it partitions as well.

* Characterize and quantify tars produced. Tars could potentially cause significant operating and environmental problems. Tar problems have been a fatal flaw for a number of biomass gasification designs. We will use the data developed to design appropriate allowances into the demonstration units.

* Characterize refractory (the unburned) carbon. What does the nature of the unburned carbon tell us about improving carbon conversion or managing the waste stream?

The lab-scale effort needs expertise in gasification kinetics and mechanisms. The Technology Summit group feels that Brigham Young University/University of Utah; the University of Maine (van Heinengen); Abe Akademi in Turku, Finland; Chalmers University; and the National Renewable Energy Laboratory (NREL) all have the requisite experience with fundamental work on gasification. The pilot-scale work should be performed in MTCI's pilot unit, with full involvement of the lab-scale work provider.

Gap No. 2: The fluid dynamics of the Big Island commercial demonstration unit create significant added uncertainty. The unique geometry of heaters and reactor vessel has not been used before. If researchers encounter problems, they will lose a tremendous amount of time in trial-and-error troubleshooting.

Fluid dynamics play an important role in heat transfer, temperature profiles, and reaction rates. As the MTCI Steam Reformer is scaled up in size, the complexity of the fluid dynamics increases tremendously.

The gap-filling technology needed is a computational fluid dynamics model of the LT-BLG system. This will create valuable knowledge for reducing risk and optimizing performance of the demonstration and first commercial unit. The scope of the effort should include the following steps:

* Incorporate kinetic data into a model of the fluid bed reactor.

* Model the fluidization and heat exchanger interaction, employing fine grid work near the tube surfaces to carefully examine local conditions.

* Assess heat transfer rates, temperature distribution, gas flow profile, particle residence time, and gas-phase composition.

The modeling called for in this work may fall outside of current experience and may require researchers to develop new techniques. Among those qualified to undertake this work are: Fluent, Chalmers University, PSL, McDermott, AWEA, and BYU/University of Utah.

Gap No. 3: We need a solution--suitable for LT-BLG conditions--that mitigates the increased causticizing load produced by the gasification process. This represents a significant cost penalty, weakening the overall economics for BLGCC.

In LT-BLGCC, nearly all sulfur partitions to the gas phase as hydrogen sulfide, while the sodium goes to the solid phase as sodium carbonate. That results in a much higher recausticizing load compared to conventional technology, since any additional carbonate loading requires lime to remove it.

The potential gap-filling technology is autocausticization. It may provide an especially elegant solution to avoid the extra recausticizing load and widen the operating temperature window, making it easier to achieve high carbon conversion. In autocausticization, a portion of the sodium in the solid phase is tied up with an autocausticizing agent, blocking the formation of sodium carbonate. Two known autocausticizing agents may be applicable in LT-BLG--titanium dioxide (Ti[O.sub.2]) and sodium borate.

To develop this concept, the group outlined the following applied research program:

* Determine the maximum operating temperature with in LT-BLG conditions.

* Assess the economics for Ti[O.sub.2]. Carry out lab-scale separation of Ti[O.sub.2] in dregs and determine all titanium compounds present in liquid and solid phases.

* Determine the fate of sulfur and chloride with Ti[O.sub.2] in LTBLG conditions.

* Determine if borate is applicable for LT-BLG conditions.

If one of the agents appears to have promising economics, it should be demonstrated on the pilot unit. It could then be included as part of the first kraft demonstration unit. (The Big Island unit processes soda semi-chem liquor, so causticizing impact is not relevant on that unit.)

This research program should be carried out with some collaboration among the following:

* University of Maine (Heinengen, who has carried out significant preliminary research on Ti[O.sub.2])

* Western Michigan University (Cameron, who has carried out preliminary work on borate)

* University of Toronto (Tran, who has consulted on actual borate applications in Tomlinson furnaces);

* US Borax (Bair);

* Chalmers University (Theliander)

* MTCI, to carry out the pilot unit work

HIGH-TEMPERATURE BLGCC GAPS

The group identified two gaps unique for HT-BLGCC and critical to its commercialization:

Gap No. 1; The first gap is the lack of a material that can survive HTBLGCC conditions. Current materials for the reactor vessel lining are inadequate. The combination of high temperatures and alkali makes the reactor lining a severe materials challenge. This challenge is made worse at the transition to the much cooler quenching section. Chemrec has used refractory in the pilot units and the commercial atmospheric units. The New Bern atmospheric BIG has experienced considerable downtime due to refractory like. For this reason, reactor vessel materials are the most serious technical obstacle to commercialization.

The performance of the most recent refractory at New Bern, fuse cast, has been encouraging but further exposure is needed to confirm its durability and service life. Fuse cast is an extremely expensive alternative and is highly sensitive to thermal shock.

Chemrec is investigating the use of a cooled-wall reactor. Even with this device, mills will need a suitable protection system for the walls. Chemrec is working to identify suitable materials for this alternative.

We need gap-filling research focused on a systematic material review and combinatorial testing program. Such a program would examine novel alloys (combinations of nickel, molybdenum, and chromium), refractory with low porosity, self-healing refractory, and coatings (such as aluminum oxide or turbine blade coatings). The most promising materials arising from the program will subsequently be tested in the New Bern BLG (or potentially the Pitea, Sweden design verification unit) and a Tomlinson furnace.

Ideally, to maximize the potential for a novel solution, the collaborators should include a number of different perspectives to this issue. Three that should be considered are ORNL, Albany Research, and Integran Technologies (MacKenzie).

Gap No. 2: The additional causticizing load for HT-BLG relative to conventional technology is a substantial cost penalty. The water-quench operation unique to the Chemrec design makes this even worse by promoting co-absorption of carbon dioxide (C[O.sub.2])that must be subsequently causticized.

In HT-BLG conditions, a substantial amount of the input sulfur partitions to the gas phase as hydrogen sulfide ([H.sub.2]S). This must be recovered for economic operation. Unfortunately, some C[O.sub.2] is absorbed (to different degrees depending on selectivity), increasing the demand for causticizing to provide useful sulfur (as sodium sulfide) for pulp cooking.

As proposed for LT-BLG, autocausticization is a potential gap-filling technology for HT-BLG. Autocausticizing may allow mills to avoid the extra recausticizing load. In autocausticization, a portion of the sodium in the solid phase is tied up with an autocausticizing agent, blocking the forrnation of sodium carbonate. Two known autocausticizing agents may be applicable to the specific conditions in HT-BLG: Ti[O.sub.2] and sodium borate.

To develop this concept, the Technology Summit working group recommends the following applied research program:

* Assess the economics for Ti[O.sub.2]. Determine the reaction kinetics for the autocausticizing reaction. Garry out lab-scale separation of Ti[O.sub.2] in dregs and determine all titanium compounds present in liquid and solid phases.

* Assess effectiveness of borate in HT-BLG conditions.

If either agent is successful, it should be demonstrated on a pilot unit. It could then be included as part of the first or second kraft demonstration unit.

The working group recommends that this research program be carried out, with some collaboration, among:

* University of Maine (van Heinengen, who has carried out significant preliminary research on Ti[O.sub.2]);

* Western Michigan University (Cameron, who has carried out preliminary work on borate);

* University of Toronto (Tran, who has consulted on actual borate applications in Tomlinson furnaces);

* US Borax (Bair);

* Chalmers University (Theliander);

* Ghemrec

* Institute of Paper Science and Technology (Sinquefield)

A second potential gap-filling technology is elimination of the water quench in the Chemrec design for HT-BLG. Avoiding the water quench step would open the opportunity to reduce the causticizing penalty and increase power production. This pathway will examine the feasibility of electrolytic causticizing of smelt (a concept proposed by Pfromm and Winnick for conventional recovery furnaces) and use of a spouted circulating fluid bed (CFB) with indirect cooling to handle the gasifier smelt. Researchers will develop preliminary conceptual designs and economic analyses. Candidates for this conceptual work are the University of Toronto, Institute of Paper Science and Technology (Pfromm), Georgia Tech (Winnick), Teledyne, and Monofrax.

Biomass Gasification CC Gaps: The group concluded that tars management is the critical barrier to commercialization. If biomass GCC is to become a breakthrough technology, this issue must be resolved.

The conditions for biomass gasification favor tars formation. This has proven to be in actual experience and has proven to be a fatal flaw in more than one demonstration project. Tars create significant downtime for cleanup and are themselves a problematic waste handling issue for mills. They also represent an efficiency loss.

Biomass gasification (without the combined cycle) is widely practiced. Tars are typically not an issue because the subsequent combustion zone is close-coupled to the gasifier, so there is no potential for unwanted tar accumulation.

The industry needs gap-filling research/technology focused oil a parallel research program into tars management that examines catalytic and non-catalytic systems. The overall program should include an investigation of recent tar management failures. The catalytic program should examine non-nickel catalysts, screen novel structures and peroskivites, and carry out demonstrations using existing nickel catalysts. The non-catalytic program should include literature review of previous approaches (including the petrochemical industry), and an assessment of separation technology for gas/liquid/solid systems. The most promising solutions should be applied in trials on the Battelle/FERCO unit at Burlington, Vermont, USA.

The best candidates for the catalytic program are: Chalmers University, Institute of Paper Science and Technology (IPST), Georgia Tech, Sandia Albuquerque, VTT (Finland), and TPS (Swedish Gasifier Group). The non-catalytic program should be conducted at NREL.

KEY TO SELF SUFFICIENCY

Commercialization of black liquor and biomass gasification/combined cycle is a key element in the industry's vision of energy self-sufficiency. Without it, the industry will be subject to supply and pricing variability of fossil fuel-based power generation. With it, the industry can position itself" to be an important supplier of "green" power. Perhaps just as important, these technologies offer the potential to create breakthrough change for the industry with crosscutting impacts from energy to pulping yield.

The industry's goal--to have commercial gasification combined-cycle products by 2008 can be realized. Gasification combined-cycle technology is on the verge of becoming a commercial reality if we act now and can drive the last critical issues to conclusion.

Acknowledgement: The author wishes to recognize the invaluable contributions of Del Raymond of Weyerhaeuser Co. to this research area and to this report.

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 

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]