Energy Analysis for Conversion of a Kraft Pulp Mill into a Dissolving Pulp Mill

Fate of wood extractives in wastewater treatment plants at kraft pulp mills and mechanical pulp mills

Pulp and paper (P&P) mills are currently one of the largest industrial water consumers and effluent generators worldwide. The biological effluent treatment processes currently in use generate a large volume of sludge (waste activated sludge – WAS), which requires great efforts and high costs to manage. An interesting option for sludge management is anaerobic digestion, a means of reducing sludge volume while generating renewable energy that can be used in the industrial processes. However, anaerobic technology needs to be improved, mainly due to the 30- to 40-day retention time required to digest pulp mill sludge in conventional anaerobic bioreactors. The thesis was structured in 3 chapters written as scientific papers. Chapter 1 presented a literature review about the potential of anaerobic digestion for sludge treatment in P&P mills and the application of pretreatment methods to enhance methane production, decrease the retention time and, ultimately, decrease the volume of the digesters. A case study examining the potential of integrating pretreatment and anaerobic sludge digestion in a Brazilian kraft pulp mill is also presented. The literature review resulted in 52 matches in which 16 articles were related to anaerobic digestion or co-digestion of P&P sludge without pretreatment and 20 articles had to do with anaerobic digestion of P&P sludge after pretreatment. A large discrepancy among the presented results made it difficult to assess the suitability of anaerobic digestion and the actual impacts of the sludge pretreatment on the viability of the system. Simulations were carried out using current data from a Brazilian kraft pulp mill and indicated the important role of sludge pretreatment in potential methane production. Chapter 2 aimed the application of thermal, thermal-alkaline and mechanical pretreatment methods in order to promote the solubilization of organic matter to enhance the anaerobic digestion. Chemical analyses showed an improvement in organic matter solubilization, with an increase greater than 1.2-fold for total COD, 7-fold for soluble COD and 4-fold for BOD 5 . In general, thermal-alkaline pretreatment showed the best results for all the evaluated parameters, with the advantage of requiring lower temperature and retention time when compared to thermal conditions. Chapter 3 aimed to evaluate the potential of methane production from the WAS of a bleached kraft pulp mill applying biochemical methane potential (BMP). After 30 days of testing, cumulative methane production increased from 90 mL CH 4 /gVS (raw sludge) to 181-194 mL CH 4 /gVS with thermally pretreated samples, and up to 203-204 mL CH 4 /gVS with samples which were pretreated using the thermo-alkaline technique. The pretreatment conditions of 175 °C for 15 min at pH 11 were sufficient to achieve both a high solubilization of WAS and a high methane production. The results showed that pretreatment could significantly enhance the anaerobic digestion of kraft pulp mill WAS, making this an attractive new option for sludge management in this sector. Keywords: Anaerobic digestion. Methane yield. Pretreatment. Pulp and paper mill. Secondary sludge.

Significant opportunities for energy savings are identified in the hot and warm water system of a kraft pulp mill. Short-term variations in the process are studied in order to identify and quantify the influences of these variations on the energy-saving opportunities. Daily and ten-minute averages of measured data are used as varying input data in a heat exchanger network with fixed heat transfer areas. When the short-term variations are considered, the total energy savings are decreased by about 10%. The steam-saving opportunities correspond to at least 5% of the mill’s total steam use, when the short-term variations are considered. At least 65% of the influences of short-term variations are detected already when the seasonal variations are considered.

Efficient energy systems with CO2 capture and storage from renewable biomass in pulp and paper mills

The potential for energy savings when reducing the water consumption in a Kraft Pulp Mill

A baseline characterization of fine particulate matter (PM2.5) concentration and releases in Nova Scotia, Canada

Carbon capture and storage (CCS) using solvent based absorption has the potential to significantly reduce the carbon intensity of power stations. It is one of a range of technologies that is necessary to be deployed in able to reduce greenhouse gas emissions at the lowest cost. However, the addition of CCS to power stations will increase the capital and operating expenditure of the power station and will reduce the net power produced from the power station. Therefore, minimising both the capital cost and the energy penalty associated with CCS will be imperative to ensuring that the cost of electricity of power stations with CCS remains competitive. This research uses multi-objective optimisation (MOO) of the CCS system applied to pulverised coal power stations using a combination of process simulation, heat integration using a linear programming form of pinch analysis and cost estimation. The benefit of combining MOO with automated pinch analysis is that the heat exchanger network does not need to be defined for the optimisation of the process synthesis. In this project, heat integration has shown to potentially lead to significant reductions in the energy penalty associated with the addition of CCS. Capturing 90 % of the CO2 in the flue gas, the energy penalty can be reduced from 38 % without heat integration, to just 14 % with a fully optimised and heat integrated solvent system. However, when the capital and operating costs are factored into the optimisation, to minimise the differential cost of electricity, the optimum level of heat integration may be more moderate, with energy penalties of between 25 and 30 %.

Process integration of near-neutral hemicellulose extraction in a Scandinavian kraft pulp mill – Consequences for the steam and Na/S balances

Heat integration techniques are now widely used for energy saving in petroleum processes. In this paper, an industrial hydrocracking process (UOP license) is retrofitted by pinch analysis as a significant tool for heat integration. The hydrocracking process is a main important conversion process in oil refineries and there has been sustained effort to improve its energy efficiency. Application of pinch analysis in retrofit of this process shows the heat exchanger network is operated efficiently. However, a large amount of energy is wasted from the hydrocracking unit, which their condition make no of use directly by the process during pinch analysis. Actually, most of the refining petroleum processes use considerably more energy than the operational minimum energy requirements because of their energy losses. These external energy losses are due to many factors, including normally inefficient or outdated equipment and process design, inadequate heat recovery, and poor integration of heat sources and sinks. However, without identifying the quality of the energy losses, it is difficult to determine how much of that energy is feasible to recover under realistic plant operating conditions. This is where exergy analysis can significantly assist in determining energy recovery opportunities. Thus, this paper is addressed to researchers who are assessing the quality of energy wasted in hydrocracking process, by using the principles of both pinch and exergy analysis. Based on the result obtained, the flue gas exhaust and the high pressure drop in reaction section can be considered as the exergy loss sources in this process. Moreover, the portion of waste energy that can be practically recovered is quantified.

Total site mass, heat and power integration using process integration and process graph

A surface coal mine in southeastern Ohio has been reclaimed with approximately 15 to 25 cm thickness of biosolids from a bleached kraft pulp and paper mill wastewater treatment plant. Soil, vegetation, rodents, earthworms, insects, fish, frogs, sediment, and algae samples were collected and analyzed for 2,3,7,8‐tetrachlorodibenzo‐ p ‐dioxin and 2,3,7,8‐tetrachlorodibenzofuran. Water samples from lakes receiving drainage from unreclaimed and biosolids reclaimed areas were collected and analyzed for various parameters, including pH and metals. The trace levels of dioxin and furan in the pulp and paper mill biosolids did not bioaccumulate in rodents, insects, or earthworms or translocate into plants living in the reclaimed area. The trace levels of dioxin and furan in biosolids did not sufficiently migrate to a drainage lake to result in significant concentrations in fish, frogs, algae, or vegetation. The biosolids reclamation resulted in dramatic decreases in spoils leaching of acid, aluminum, calcium, iron, magnesium, manganese, nickel, and zinc. This work supports the thesis that surface mine reclamation with pulp and paper mill biosolids is safe and effective.

Methanol Production From the Pulp Mills and Paper Industry

Waste handling is a concern in all pulp and paper mills. Best available techniques for reducing waste is to minimize the generation of solid waste and/or reuse these materials, wherever practicable. One of the most important solid wastes is lime mud which is generated from the kraft pulping in its chemical recovery process. This paper explores the composition of lime mud resulting from the chemical recovery unite of kraft pulp mill and investigation of this waste for re-using beneficially on sub grade and pavement of forest road as a alternative disposal method. Lime mud obtained from the re-causticising process in SEKA pulp mill that utilizes wheat straw and reed as the principal raw material was supplied with % 47 water content and its chemical and physical characterisations was performed according to standard methods. Dried waste to environmental condition was mixed with certain amount to composite cement for using on pavement and sandy clay, loamy clay and clay soils for enriching forest road sub grade properties. In order to investigate the lime mud addition on pavement and sub grade properties necessary physical tests were performed. As a consequence this study reveals that while waste of lime mud causes environmental and economical problem with conventional disposal techniques and/or abandoning to environment, this waste can be used as good stabilisation materials on forest road sub-grade and pavement without any environmental problem.

Phytoplankton and macroinvertebrate assemblages were used to assess the impact of a kraft pulp and paper mill effluent in Kenya, on River Nzoia downstream of the discharge point in relation to changes in water quality during May to June and November 2008 (rainy and dry seasons, respectively). Total phosphorus concentration increased from 0.027 mg.L-1 upstream to 0.04 mg.L-1 downstream. Ammonia nitrogen (NH3-N) concentration was 0.51 mg.L-1 upstream and 0.86 mg.L- 1 downstream. Nitrate concentration stood at 1.18 mg.L-1 upstream compared with the 2.23 mg.L-1 downstream. The pH changed from 4.5 to 5.0 upstream to 5.5 to 6.0 downstream, while DO increased from 6.57 to 7.03 mg.L-1 downstream. The BOD5 (biochemical oxygen demand after five days) values remained almost unchanged from 4.63 mg.L-1 upstream to 4.67 mg.L-1 downstream. Taxon composition of phytoplankton and macroinvertebrates correlated with adverse environmental gradients resulting from the mill's effluent discharge. Overall, there was a shift in composition and abundance of both phytoplankton and macroinvertebrates, with the downstream site recording high numbers of tolerant taxa (i.e., Microcystis sp. and Chironomus sp.). It was recommended that water quality monitoring with effluents of this nature be done using a combination of chemical analysis and biological indicators such as phytoplankton and macroinvertebrates.

Principal-components analysis (PCA) was used to compare concentrations of polychlorinated dibenzo-p-dioxin (PCDD) and polychlorinated dibenzofuran (PCDF) compounds in sediments collected from two interconnected lakes, Lake Champlain and Lake George, New York, USA. Two different PCDD/PCDF congener profiles were present in surface sediment samples from Lake George. Samples collected near residential areas and power-boat marinas had elevated hepta- and octa-CDDs (1±0.3 ng/g) and tetra-octa-CDFs compared with samples collected in other areas of the lake. The PCDD/PCDF pattern in the high-level samples was similar to the PCDD/PCDF pattern in sediments from Green Lake, NY, a small lake in which atmospheric deposition is the only route for PCDD/PCDF contamination, either from local sources or from long range transportation from multiple sources in the midwest. The samples containing the higher PCDD/PCDF concentrations also contained higher lead concentrations (173±33 μg/g) compared to the low-level PCDD/PCDF samples (52±25 μg/g). However, the increase in lead concentrations was accompanied by increased concentrations of other trace metals. Consequently, it can be concluded that emissions from power boats are not responsible for the PCDD/PCDF contamination in Lake George. Concentrations of PCDDs/PCDFs in the low-level samples were similar to PCDD/PCDF concentrations in sediments from remote midwestern lakes where long range atmospheric deposition was the only plausible route of entry for the PCDD/PCDF compounds. However, other studies have shown that offshore sediments in Lake George have lower concentrations of organic carbon than inshore samples and, therefore, the low-level PCDD/PCDF pattern may be an artifact related to a reduced PCDD/PCDF concentration in sediments with a low organic carbon content. Surface and core sediments from Lake Champlain also partitioned into two groups, which both had PCDD/PCDF patterns differing from the high-level surface sediments collected from Lake George. The largest group of samples was characterized by the presence of high octa-CDD concentrations (3.5–18 ng/g). The second group of samples was four sections from a single core sample collected near a bleached kraft pulp and paper mill, which closed in 1970. These samples had high concentrations of tetra-CDFs (0.5–1.4 ng/g), primarily 2,3,7,8-tetra-CDF, accompanied by comparable concentrations of octa-CDD (0.9–4.4 ng/g). The presence of 2,3,7,8-tetra-CDF is consistent with results from several studies where PCDDs/PCDFs were analyzed in samples taken from various stages of the bleached kraft process. These samples were grouped in the same quadrant on a PCA plot as coal soot and pulp and paper mill sludge. However, the grouping was not close, and the PCDD/PCDF contamination in these sediments cannot be associated with either source. Five sections of a core collected near a currently operating bleached kraft pulp and paper mill also had elevated 2,3,7,8-tetra-CDF concentrations (0.3±0.05 ng/g), but these 2,3,7,8-tetra-CDF concentrations were accompanied by considerably higher octa-CDD concentrations (7.5±0.5 ng/g). Therefore, they could not be distinguished by PCA from the majority of the Lake Champlain samples.