Main Task in Plants’ Energy Assessment
Thorough review of all process design, licensors schemes, systems drawings, data analysis documents to form the total-site big picture Meet and discuss with all project parties to understand all soft constraints (plant operators preferences and so on) to depict desired level of the final plant design “Acceptability Index”.
Understand the process energy needs and utility systems preferences of both the new plant and the existing one, if applicable Understand the interaction among the process and both the heating and cooling utility systems.
Understand the interaction between the site and beyond the fence site(s).
Establish with the project’s owners objectives/targets and constraints for the new project fuel, power, steam, water and refrigeration consumption and/or generation landscape.
Identify all opportunities for energy savings in the base case design. Define savings related to better plot plan and optimal multi-generation schemes. Challenge every process step in the base case design to generate new process alternatives for the sake of lower energy system operating and capital cost.
From available data, establish different process-utility design schemes that can render better energy consumption, less number of units, less process-utility systems capital cost and in general better economic solutions.
Propose scope for definitive assessment for the new process-utility systems cheme(s) including the most accurate economic analysis.
Present the plant-wide energy utility systems synthesis.
Discuss findings with engineering contractor and project team besides other concerned parties before issuing the final report. Regarding the power and heat supply decision; it is essential to address it in addition to the process optimization for energy efficiency improvement and give recommendations regarding the question of using cogeneration or not, to satisfy the process heat and power supply.
1. Data extraction for the study to be done for each stream that needs to be heated or vaporized and any stream that needs to be cooled or condensed in the “base design case”. As if each stream will be handled through utilities. (No integration in the base case design).
2. Calculate targets for energy utility to be calculated for the process with integration and without integration.
3. Establish the process grand composite curve for the base case design to be utilized to help show the right/optimal level of utility mix, for heating and cooling utilities.
4. The grand composite curve (GCC) as an essential tool in the pinch technology packet (will be explained later in the book) needs to be utilized to show the potential cogeneration opportunities and best drivers for the process, if any.
5. Constructing the site- source and sink composite curves
6. List all possible design and operational modifications to be investigated to explore its impact on the utility consumption and other process units.
7. The above steps should be done for several ΔTmin., before selecting the optimal. Of-course in such cases a preliminary evaluation of the HENs capital cost will be needed, or whatever targeting method you use, to reach the close-to-optimum ΔTmin.
8. Preliminary HEN synthesis developed will render several process initiatives for improving the design from energy efficiency point of view compared with the base case design.
9. The process scheme(s) produced may have some environmental, safety and control/operability constraints that may justify forbidding streams matching and warrant the removal of some streams from the heat integration schemes or even removing all of them from integration scheme; it does not matter as long as the design is pursued systematically and the techno-economical justifications are detailed and documented.
10. One-by-one, of “problem” stream(s) shall be taken out from the integrated process scheme and its energy impact in “Dollars” is defined. In the same time an engineered solution for solving this problem/ constraint, safety; control/operability or other problem, shall be suggested and its impact shall also be roughly quantified/estimated in Dollars if possible and documented.
11. Trade-off between the energy saving impact “$” and for instance the control/operability impact $ shall be calculated, documented and shown in the energy assessment study.
12. Other subjective decisions need to be mentioned and documented clearly with enough techno-economical support as much as possible to support the decisions of accepting or rejecting process initiatives for the sake of energy efficiency optimization.
In order to get the best out of any energy assessment study for grassroots facility, we suggest that you explore the most important modifications that would have the highest impact on the base case design from energy efficiency point of view and/or the ones that can also save capital cost. Most of the time modifications which have less impact on the project schedule take the front seat.