Steam and water combined analysis, integration, and efficiency enhancement in Kraft pulping mills

The principle objectives of this thesis are divided into two main parts. The first key objective is to develop new process integration (PI) techniques to individually improve the efficiency of water and steam systems, the performance of equipment, and the heat exchanger (HEX) network of the existing water-based process. These techniques are validated by applying them to the Kraft process. The second objective is to develop a steam and water analysis enhancement and integration (SWAEI) methodology to improve the energy and water efficiency of a water-based process by combining the new PI techniques.;The Kraft pulp and paper (P&P) mill is one of the major water and thermal energy users in the Canadian industrial sectors. It is also one of the water-based processes where there is large interaction between water and steam systems.;The first developed PI technique is simultaneous energy and water networks analysis (SEWNA) that involves five steps to save steam and water at the same time. A new approach to identify the control volume for data extraction is shown. Inevitable effluents from the source pool are subtracted to prevent accumulation of chemicals and unwanted particles. In the process line, the potential for steam saving is determined considering the existing process constraints for water utilization and filtrate reutilization. The new rules for filtrate reutilization are presented. The new water and energy analysis can be performed either in tabular or graphical form to identify the water measures with respect to steam reduction. The new graphical Water and Energy Pinch Curves consist of contaminant concentration and temperature curves versus flowrate for all sinks and sources. The saved water is reduced systematically from the origin source of the hot and warm water production network. This eliminates steam consumption for hot/warm water production and also provides hotter and warmer water using the existing HEX network. Finally, the economic analysis is conducted to calculate the piping cost for new water reutilization connections.;The second developed PI technique is equipment performance analysis (EPA). It characterizes, analyzes, and diagnoses individual equipment or departments from the standpoint of steam and water consumption. The key performance indicator (KPI) for energy and/or water efficiency of equipment or a department is calculated and benchmarked against reference data. Probable causes and solutions are determined for inefficiencies. This technique has been applied to mill C.;The third new PI technique is the retrofit HEX network design (R-HEN) for a water-based process that consists of four successive steps. The physical and process constraints including hard and soft temperature of sensitive unit operations are analyzed. A realistic targeting for steam saving is conducted based on the constraints and the classification of steam users. The existing process stream HEXs are assessed to be used effectively in the new network. To utilize efficiently the heat of waste streams, they are categorized as high and low corrosive. The retrofit HEN is designed using a new algorithm according to five heuristic and practical rules.;The steam and water analysis enhancement and integration (SWAEI) methodology consists of six successive steps. In the first step, the simulation model of the base case is developed. In the second step, pre-benchmarking is carried out by comparing the steam and water consumption with reference data. The core of methodology is the identification of the energy and water improvement projects by sequentially applying SEWNA, EPA, and R-HEN. Sequential application of these techniques results in significantly more steam saving than if they would have been applied individually. This sequential application leads to complementary projects to maximize steam saving. The excess steam is used to reduce or eliminate fossil fuel consumption. The remainder of excess steam could be sold to the local district, generate electricity using cogeneration or a combination of cogeneration and an absorption heat pump (trigeneration) system. These alternatives for using the remainder of excess steam are examined from the economical perspective to choose the most promising one for implementation. In step five, the identified projects are prioritized and the implementation strategy is proposed in two phases. In phase one, it is proposed to implement the projects that lead to fossil fuel reduction or elimination. The other projects are proposed to be implemented in the second phase to save more steam for selling or generating electricity. Finally, the post-benchmarking is conducted to visualize areas of improvement. The methodology has been applied on three mills and yielded 27, 33, and 66% steam savings and 38, 24, and 58% water savings for mills A, B, and C, respectively. (Abstract shortened by UMI.).