Heat Integration Opportunities Research Articles

Heat integration of an Olefins Plant: Pinch Analysis and mathematical optimization working together

This work explores a two-step, complexity reducing methodology, to analyze heat integration opportunities of an existing Olefins Plant, identify and quantify reduction of energy consumption, and propose changes of the existing heat exchanger network to achieve these goals. Besides the analysis of plant design conditions, multiple operational scenarios were considered to propose modifications for handling real plant operation (flexibility). On the strength of plant complexity and large dimension, work methodology was split into two parts: initially, the whole plant was evaluated with traditional Pinch Analysis tools. Several opportunities were identified and modifications proposed. Modifications were segregated to represent small and independent portions of the original process. One of them was selected to be re-analyzed, considering two scenarios. Reduction of problem dimension allowed mathematical methodologies (formulation with decomposition, applying LP, MILP and NLP optimization methods) to synthesize flexible networks to be applied, generating a feasible modification capable of fulfilling the proposed operational scenarios.

Heat Integrated Distillation System Design

Distillation is the largest single energy consumer in the chemical process industries. However, distillation does not consume energy but degrades the heat input to the reboiler that is subsequently rejected in the condenser. The most effective way to reduce the energy consumption of distillation is by effective heat integration. However, the distillation design and operation must be considered simultaneously with its heat integration. For single distillation columns it is straightforward to identify appropriate heat integration opportunities. For complex distillation systems, the most appropriate combination of distillation system design and operation and heat integration are far from straightforward. The whole separation system together with its heat integration and utility system must be considered simultaneously. This presentation will explain new approaches to be design of heat integrated distillation systems. Examples will be developed from crude oil distillation and from low-temperature separation in chemicals production. Copyright ? 2010, AIDIC Servizi S.r.l.

Sequential Methodology for Scheduling of Heat-Integrated Batch Plants

Optimal scheduling of tasks to be performed in different unit operations is of paramount importance in the batch processes. The pressure toward sustainable operation has warranted more attentions to be paid to the issues of heat integration to reduce the utility consumption. This paper presents a new approach for incorporating heat integration in batch process scheduling. The method is based on a sequential framework, where the overall problem is decomposed into two sequentially solved problems of scheduling and heat integration. First, the schedule is optimized to meet the economic objective such as makespan or profit. Next, alternate schedules are generated through a stochastic search-based integer cut procedure that adds further constraints to the scheduling formulation. Such schedules may be the alternate optima of the scheduling problem. Finally, heat integration analysis coupled with the time average model (TAM) and time slice model (TSM) is applied to each of the resulting schedules to establish the minimum utility targets. The approach is based on the precept that opportunities for heat integration between tasks are higher in near-optimal schedules where tasks are temporally clustered together. The method differs from other sequential approaches published in the literature in that the heat integration problem is solved with the intent to retain the optimality of the scheduling solution. The proposed method has the ability to handle problems too complex to be solved using simultaneous optimization approaches. It has been applied to two literature case studies. The first one involves profit maximization as the objective function. The second one entails a more complex scenario involving makespan and utilities. The results from both case studies demonstrate the effectiveness of the approach.

Heat integration opportunities in an average Scandinavian fine paper mill: model study and comparison with a market pulp mill

The pulp and paper industry has a potential for significant energy savings, as shown by many studies on both market pulp mills and integrated pulp and paper mills. In this study, we compare the opportunities for energy savings through heat integration in the two mill types. To do this systematically, we used model mills with an identical pulp mill connected to either a pulp dryer or to two paper machines. An energy analysis of the integrated mill showed that there are steam-saving opportunities of about 16%, which enable increased electricity production or fuel savings in the form of reduced bark burning. For electricity production, the break-even electricity price was 25–50 €/MWh depending on economic conditions. For fuel savings, the break-even bark price was 5–11 €/MWh depending on economic conditions and electricity price (the electricity production decreased when fuel was saved). When comparing the integrated pulp mill with the market pulp mill, the authors identified inherent differences that influenced the steam-saving opportunities in favor of the market pulp mill, implying a payback period about 0.4 years longer in the case of electricity production in the integrated mill. In the case of fuel savings, however, the integrated mill would have significantly better profitability, because fuel savings in the market pulp mill had to be in the form of lignin extraction from the black liquor, which would entail additional investment and operating costs.

Heat integration opportunities in average Scandinavian kraft pulp mills: Pinch analyses of model mills

Article Heat integration opportunities in average Scandinavian kraft pulp mills: Pinch analyses of model mills was published on November 1, 2006 in the journal Nordic Pulp & Paper Research Journal (volume 21, issue 4).

Optimal scheduling of heat-integrated multipurpose plants under fouling conditions

This work presents a systematic mathematical framework for scheduling the operation of multipurpose plants involving heat-integrated unit operations under fouling considerations. A salient characteristic of this problem is that the performance of each heat-integrated unit, which decreases with time due to fouling, can be restored to its initial state by performing cleaning operations. Based on a uniform time discretization, the overall problem is formulated as a mixed integer non-linear programming (MINLP) model. An iterative procedure is proposed for the solution of the resulting non-convex MINLP model, involving the solution of a series of mixed integer linear programming and non-linear programming subproblems. The optimization algorithm determines simultaneously: (i) the production schedule, (ii) the number of cleaning operations required along with their corresponding timings, (iii) the optimal utility utilization profile and (iv) the heat transfer medium flow rate profiles over time. An example problem is presented to illustrate the applicability of the proposed approach. It is proved that fouling considerations can significantly affect the production schedule as well as heat integration opportunities.