Development of integrated forest biorefineries

An Integrated Forest Biorefineries (IFBR) is the coupling of different biorefinery technologies that utilize lignocelluloses feedstock, with existing pulp and paper mills. In an IFBR with a Kraft pulp mill as the receptor process, the cellulose fraction of the wood feedstock is dedicated to pulp production while part of the lignin and hemicelluloses fractions can be extracted and transformed into value added products for the biorefinery. It is necessary that the extraction of these fractions do not negatively impact the pulp production capacity, chemical balance, power generation and production cost of the base pulping process. The IFBR should be capable of producing a broad spectrum of biochemical, biomaterial and /or biofuels.

Several studies on the integration of biorefineries with existing pulp and paper mills are ongoing. Pulp and paper mills especially Kraft pulp mills are ideal receptors for the integration of biorefinery processes because paper mills have vast experience with securing, handling and processing of biomass, they are situated in proximity to numerous sources of biomass, their thermal efficiencies can be improved to liberate enough for a biorefinery and some mills already have experience with the production of energy from biomass [40].

Different authors have highlighted the motivations, benefits and challenges that need to be surmounted in order to achieve successful integration of a biorefinery as shown in Table 1.3. Although some of the reviewed literature stated slightly varying justifications for why an integrated forest biorefinery should be set up, the reasons are all in mutual agreement and do not stand in contradiction with each other

Table 1.3: Motivations for developing integrated forest biorefineries

Incentive Challenges (C)and/or limitations (L) Source

 Diversification of business model

 Transformation of the enterprise (C)

 Selection of best product and product portfolio (C)  Phasing of biorefinery implementation (C)

Chambostet al. [41]  Energy affordability

 Reduced environmental impact of energy supply

 Shortage of capital for integration (C)

 Based on syngas / Gasification only (L) Connor [40]  Reliable energy supply

 Reduction of emissions  Energy security over the

importation of energy

 Protection of core business of the industry (C)

 Leveraging on the rare alignment of societal and industrial interests (C)

Closset et al. [42]

 Changes to how forest resources will be processed and utilized

 Research still needed for available technologies to reach level of commercialization (C)

 Distinguishing between classes of products (main products, co- products & by products) and their long term interrelationship (C)

Söderholm et al. [43]

 Energy supply assurance  Potential life cycle of plant (C)

 Identifying the best pathways for production (C)

 Identification of best projects by comparison of alternatives (C)

Thorpet al. [44]

 Reduced pulp and paper production cost

 Diversification of revenue sources for pulp mills

 Smooth integration (C)

 Ascertaining the impact of modernizing a mill (C)

 Determining the order of magnitude of different biorefinery cases

Hytönen et al. [45]

An incentive, which stands out from other sources is that biorefinery integration leads to reduced pulp and paper production cost by Hytönen et al. [45]. The focus of biorefineries has shifted in the past 5 years from focusing mainly on biofuels production to the inclusion of biochemicals and biomaterials, despite a smaller market size than for biofuels.

Some types of biorefineries that have been proposed for integration with a Kraft pulping process are gasification, lignin extraction and hemicelluloses extraction [46].

1.4.3.1 Gasification Based Biorefineries

Gasification is the conversion of low quality solids such as wood residue and low quality liquids such as black liquor into a fuel gas. The fuel gas is referred to as either synthesis-gas or syngas and comprises mainly of hydrogen and carbon monoxide. Fuel gas can be combusted in gas turbines for the production of electricity. Products that can be obtained from syngas include Fischer-Tropsch liquid (FTL), Dimethyl Ether (DME), and Mixed alcohols (MA). Consonni et al. carried out a study on gasification based biorefineries for the pulp and paper industry and

concluded that for products such as FTL and DME, the technology for gasification exists commercially and is being used in other non-pulp industries [47]. The challenge for a gasification based biorefinery lies in the integration. Only MA still requires much research on the production technology side. Black liquor gasification has also been proposed by Naqvi as an alternative to the Tomlinson recovery boiler for improving on safety , energy efficiency and the flexibility of a pulp mill [48]. Recently explored technologies for black liquor gasification include the Booster System and the Black Liquor Gasification Combined Cycle System (BLGCC) by Chemrec [49] as well as the the Carbo-V® process developed by Choren [50].

1.4.3.2 Lignin Based Biorefineries

The lignin fraction of the wood fed to Kraft pulp mills end up in the black liquor that is normally concentrated using multi-effect evaporators before combustion in recovery boiler to produce energy. In several cases, the recovery boiler operates at its maximum thermal load and cannot be upgraded or replaced due to the high costs. This limits the pulp production capacity of the mill. The recovery and acid precipitation of lignin can be used for increasing the production capacity [51]. In addition, lignin based chemicals such as poly-urethane and vanillin, which can lead to increased revenue, can be produced. Some processes for lignin precipitation include the LignoboostTM _{process developed by Innventia and more recent LignoForce System}TM _developed

by FPInnovations [52, 53].

1.4.3.3 Hemicelluloses Based Biorefineries

In Kraft pulp mills, most of the hemicelluloses content from the wood feedstock is dissolved along with lignin during pulping and combusted in the recovery boiler. A better use of the hemicelluloses can be achieved by their extraction prior to pulping and subsequent conversion into value added products. To extract the hemicelluloses, a prehydrolysis step, which is also used in a dissolving pulp mill, is required. The prehydrolysis condition must be optimized to maintain a high pulp yield and maintain the pulp quality (fibre strength, length, bleachability). The composition of the generated prehydrolysate stream must also meet the requirement for the subsequent transformation process. To successfully develop an IFBR, all the steps required for the implementation (the extraction of hemicelluloses, conversion into value added product and the integration of the biorefinery process with a receptor pulp mill) must be studied collectively. Currently, there is limited information on such studies.