Black Liquor Gasification Can Help Sustain Forests, Generate Ultra-Clean Biofuels

By Richard J. LeBlanc
Globally, renewable automotive fuels are increasingly promoted with the help of tax credits, certificates systems and legislated mandatory use. The primary goals are increased supply security and reduced net emissions of greenhouse gases (GHGs). A vastly increased production and use of biofuels is not, however, unproblematic. To ensure the long-term viability of biofuels, their production and use must meet some fundamental requirements:

›The raw material production must have a high sustainable land use efficiency to enable a high production volume on the limited land area available; use minimal resource for cultivation; give low direct and indirect GHG emissions from cultivation; and preferably not use prime agricultural land to minimize competition with food production.

›The conversion efficiency of the raw material to the biofuel must be high.

›The engine efficiency when using the fuel must be high.

›The cost of the biofuel must be competitive.

Only when these criteria are met will it be possible to produce truly meaningful volumes of biofuels that will have a large positive impact on our supply security and GHG emissions and without other severe negative effects.

Black liquor gasification is a well-developed cellulosic biofuels technology that shows outstanding results when evaluated against these criteria.

The Technology
Gasification has long been used to convert coal, oil and natural gas into syngas containing the building blocks of valuable fuels and chemicals. Black liquor is a byproduct of the kraft pulp production process and also an excellent gasification feedstock for syngas production. Black liquor consists of dissolved wood substance, mostly lignin, and spent pulping chemicals. It is traditionally burned by mills in a Tomlinson-type recovery boiler to produce steam to drive the pulp mill processes and to recover the spent pulping chemicals. A gasification-based biofuels unit added to an existing pulp mill includes mostly well-proven technology extensively used in the petrochemicals industry. The building blocks are:

›An oxygen plant

›A black liquor gasifier and gas cooler/steam generator

›A plant for removing carbon dioxide and hydrogen sulfide from the raw syngas

›A fuel synthesis plant where liquid fuel is synthesized from the syngas

›A distillation plant where the fuel produced is purified to meet product specifications.

The patented Chemrec process, when added to a kraft pulp mill, converts black liquor, a mill byproduct, into syngas, the building block of renewable fuels and biochemicals. The gas cooler removes particulate matter and cools the gas before the next stage removes carbon dioxide and hydrogen sulfide from the raw gas. Other processes in an integrated biorefinery use established technologies already proven in the petrochemicals industry.


Producing and Using Biomass Efficiently
The concept also includes a conventional biomass boiler to make up the energy deficit that otherwise would result from the export of energy-rich biofuel from the pulp mill. In essence, a feedstock swap is made-the ideal gasification feedstock black liquor is withdrawn from the pulp mill and replaced by any kind of low-grade biomass. The boiler fuel could be forestry or industrial wood waste, agricultural waste such as corn stover or wheat straw, purpose-grown biomass such as switchgrass or willow or even the organic fraction of municipal waste.

When using purpose-grown biomass, the only quality requirement is that the biomass burns well in a boiler. This means that the selection of what to grow can be based solely on productivity, production cost and the environmental impact of the cultivation. Also, all parts and constituents of the biomass can be utilized. The result is very high land-use efficiency both in terms of amount of fuel possible to produce per acre and year and in terms of being able to use marginal land and low-input production methods, all important for sustainable biofuels production. These are aspects that become even more important when the hot issue of GHG release from indirect land-use change is taken into consideration.

High Efficiency, Low Emissions
Not only does the process have high energy feedstock flexibility, it can also produce a variety of green fuels, including dimethyl ether (DME), methanol, ethanol, synthetic diesel, synthetic gasoline and biogas.

Biofuels from a black liquor gasification process excel in terms of well-to-wheel carbon dioxide emission reduction and energy efficiency. This was confirmed by an extensive European study performed by the research institutes of the auto and refinery industries and the Joint Research Centre of the European Commission. The study included many different feedstocks, conversion processes and fuel products. Synthetic diesel and DME from forest harvest residues over the black liquor gasification route both showed among the highest well-to-wheel greenhouse gas reduction and energy efficiency.

The total available black liquor volume in the U.S. is with the conversion efficiency of this process, equivalent to approximately 5 billion gallons per year as ethanol. The renewable fuels standard calls for 16 billion gallons of cellulosic biofuels by 2022 so this route can give a significant contribution to meeting this target.

Transforming the Pulp and Paper Industry
U.S. pulp and paper companies today are meeting fierce competition from low-cost producers overseas and from alternative solutions in both packaging and printed media. Mill operators and their investors now have a viable option for breathing new life into the industry by transforming mills into biorefineries that use this fuels-from-the-forest process.

This transformation completely alters a pulp mill's competitive position by adding 30 percent to 50 percent of profitable revenue with the typical 25 percent to 40 percent internal rate of return. It also makes needed reinvestment possible by replacing aged recovery boilers with high-maintenance costs and low performance. In many cases, the fuels plant investment can also be used to provide additional recovery capacity allowing for higher pulp production.

Mills producing as little as 500 tons of black liquor solids per day are viable as fuels-from-the-forest biorefineries using this method. Most mills are considerably larger. At the minimum capacity size, such a biorefinery mill would produce upwards of 8 million gallons a year of green motor fuel calculated as gasoline equivalents.

At a mill investing in second-generation biofuels technology, jobs are not only preserved, but additional jobs are created, primarily for the extraction of biomass from the forest as well as to operate and maintain the biofuels plant. Other economic and public opinion benefits are considerable as well, such as possible tax benefits and air emissions reductions.

Typically, a capital investment for a biorefinery project that uses fuels from the forest is $200 million to $400 million, depending on plant size and the costs to interconnect to the mill. While investment scenarios can vary, a common one is collaboration of funding from the technology provider, the mill itself, investors, and state and federal grants. The black liquor gasification industry is actively pursuing federal and state grants and loan guarantees to ramp up this technology as quickly as possible to large-scale commercial capacity.

As a source of ultra-clean, renewable motor fuels, the black liquor biomass gasification route that transforms pulp and paper mills into biorefineries is standing up to critical scrutiny as a viable and practical way of producing alternative, renewable energy, while making good use of the land and being gentle to the environment.

Richard J. LeBlanc is CEO of Chemrec AB and its North American subsidiary, Chemrec USA. Reach him at [email protected].