(119b) Capital Cost Targeting of Total Site Heat Recovery

Heat recovery on Total Site level can provide a considerably high potential for energy saving. It offers additional degrees of freedom for heat recovery and cogeneration. A key issue in Total Site heat recovery is to select the minimum allowed temperature difference (ΔT_min) specifications on a site to enable obtaining realistic and useful heat recovery targets for the individual processes and the entire Total Site. The ΔT_min specifications are part of the trade-off between the rate of heat recovery and the involved capital cost, most often represented by the expenditure for heat transfer area.

Several works enable the evaluation of this trade-off for an individual process, accepting a single ΔT_min specification. Methods for targeting capital and total cost of Heat Exchanger Networks were initially developed by Townsend and Linnhoff (1984) and elaborated by others (Ahmad et al., 1990; Colberg and Morari, 1990; Linnhoff and Ahmad, 1990; Kravanja et al., 1997). A recent work (Fodor et al., 2010) has explored Total Site heat recovery targeting using multiple ΔT_min specifications for individual processes and process-utility interfaces. It is also possible to define and use the ΔT_min contributions of individual process streams in a process (Kravanja et al., 1997).

The current work deals with additional components enabling the estimation of the trade-off between heat recovery and capital cost targets for Total Sites – the evaluation of the capital costs for the generation and use of the site utilities (e.g. steam, hot water, cooling water). The paper presents the construction of the Total Site Profiles and Site Utility Composite Curves, the identification of the various utility generation and use regions at the profile-utility interfaces of the curves, followed by the identification of the relevant enthalpy intervals within those interfaces. Further, the estimation of the required minimum heat transfer surface area is performed alongside the minimum required number of utility generation and utility supply heat exchangers.

  References

Fodor Z., Varbanov P., Klemeš J., 2010. Total Site Targeting Accounting for Individual Process Heat Transfer Characteristics. Chemical Engineering Transactions, 21, 49-54, doi: 10.3303/CET1021009 .

Kravanja Z., Glavic P., 1997. Cost Targeting for HEN through Simultaneous Optimization Approach: A Unified Pinch Technology and Mathematical Programming Design of Large HEN. Comput. Chem. Eng., 21 (8), 833-853.

Townsend D.W., Linnhoff B., 1984. Surface area targets for heat exchanger networks. IChemE 11^th Annual Research Meeting (Bath, U.K., April).

Ahmad, S., Linnhoff, B., Smith, R., 1990. Cost optimum heat exchanger networks: 2. Targets and design for detailed capital cost models. Computers & Chemical Engineering, 14(7), 751–767.

Colberg, R.D., Morari, M., 1990. Area and capital cost targets for heat exchanger network synthesis with constrained matches and unequal heat transfer coefficients. Computers & Chemical Engineering, 14(1), 1–22.

Linnhoff, B., Ahmad, S., 1990. Cost optimum heat exchanger networks—1. Minimum energy and capital using simple models for capital cost. Computers & Chemical Engineering, 14(7), 729–750.