Student

Topic:

Optimised Waste Heat Recovery through Pinch Analysis and Energy Storage; A Mineral Processing Example from Europe.

Synopsis:

Within the process industry, the production of mineral products consumes a substantial amount of energy. Hereby, a Pinch Analysis can show the optimal overall plant configuration the maximum possible heat recovery and thus, leading towards significant cost savings.

The following case study analyses a mineral production facility in Europe with an existing district heating network which uses the facility’s waste heat to supply two nearby villages.

The Pinch Analysis shows the economic optimum for the investment and operational costs by proposing a thermal energy storage which leads to annual savings of over 250000 € and 700 t CO₂

Takeaways:

• Holistic systematic approach and holistic optimization (system design, energy supply, operating costs and capital costs)
• Statement regarding the absolute energy savings potential
• Prevents poor investments into incorrect efficiency measures such as the false integration of a heat pump
• Provides key data on how energy supplies, including solar energy and/or energy storage units, can be effectively implemented or dimensioned
• Shows where the current energy requirements of the process are; an element of Energy Management Systems

Submission:

Within the process industry, the production of mineral products consumes a substantial amount of energy. Hereby, a Pinch Analysis (PA) can show the optimal overall plant configuration the maximum possible heat recovery (HR) and thus, leading towards significant cost savings.

Developed in the 1970s by Bodo Linnhoff the PA is a powerful tool to optimise whole production plants in order to reduce their primary energy consumption. If a PA is conducted over a production process, it shows the total energy needed for the ideal process and ways to achieve this ideal state within the current non-ideal process. Applying economic values for all the process steps and possible improvements, it will also show the trade-off between investment- and operating costs. This is achieved by a systematic approach as follows: First, the system to analyse has to be define. As the approach of a PA is to step back from the existing configuration of the process plant, it is important to decide, which system needs to stay untouched. However, the more holistic the focus is, the bigger the achieved energy savings will be. The second step is to define the process requirements and the financial parameters for the existing Hot and Cold Utilities (HU and CU). Thus, it is crucial to question every process stream about its required temperature level to minimise external energy needed. After the scope is set and the requirements defined, the new heat exchanger network (HEN) can be constructed. Thus, showing the new optimised plant configuration and its resulting energy consumption. Energy saving is somewhat an everlasting process and most often, the focus lies on optimisation single equipment. However, the PA as one of the few theories of process optimisation shows the total theoretical energy savings possible, based on thermodynamic laws. Thus, one can directly see, how close the optimum HEN is to the theoretical potential of HR. It is clear that combined with the financial parameters to construct the new HEN, the optimal HR is a trade-off between utility costs and the payback period of the new measurements.

The following case study analyses a mineral production facility in Europe with an existing district heating network. Fed with the waste heat of the production plant, it provides part of the heat energy demand for the company’s production and administration. Furthermore, the district heating network supplies several single and multi-family houses, as well as industrial enterprises and school buildings in two villages nearby. During production breaks on the weekends and during the week when demand for heat energy exceeds supply, oil boilers are used to handle the deficit. Thus, providing over 3.8 GWh thermal energy over a standard year.

Measurements have been carried out over 3 weeks, showing that the oil burners provide thermal energy during the week even though the heat recovery potential would be more than sufficient to cover it fully on its own. Therefore, there is a significant amount of waste heat unused which dissipates to the environment.
Furthermore, the conducted PA shows first, that through internal process optimisation the coke-heated melting furnaces could save another 8% of its demand leading to savings of over 200 000 € a year. Second, that an unused HR potential of over 5 MW thermal energy exists which could be used to increase the waste heat usage by the district heating network and thus, by reducing the oil burners activity leading to a significant CO₂ emission reduction.

Based on the measurement, a simulation of the district heating network is being conducted, showing the different heating demand over the different seasons (see Figure 1). By changing the inlet as well as the outlet temperature level of the heating network, the usage of a hot water storage would become feasible. With a tank of 2800 m³, a cover rate of over 96% could be achieved (see Figure 2) and more than 3.5 GWh thermal energy be saved during the year and distributed over the weekends. Hence, leading to reduced oil burner activity and to annual savings of 250 000 € and saved CO₂ emissions of over 700 t.
Further, the district heating network could be extended and provide another 200 dwellings with affordable and clean thermal energy from waste heat. With a payback time of 6 years the project is economically feasible and contributes to a smart cities strategy where industrial waste heat is transformed to useful heat for citizens.

Hereby, the PA is a powerful methodology to show the optimum plant configuration and the achievable energy savings together with the payback period of the proposed measurements.

About David Guthorl:

David recently graduated with first class honours from the masters programme Energy Management from Dublin Institute of Technology (DIT). In summer 2017 he will graduate from his second masters programme in Energy and Environment from Lucerne University of Applied Science (HSLU) in Switzerland. At HSLU, David has also worked as a consultant in process optimisation and pinch analysis.

He started his career with an apprenticeship as an architectural draftsman in Switzerland. Upon completion he planned and supervised the construction of   multiple dwellings in the Energy Efficient Design (EED) standard. In his subsequent undergraduate studies in Mechanical Engineering at HSLU in Lucerne with a specialisation in Renewable Energies, he optimised a district heating network by installing an energy storage system.

With his in-depth knowledge of district heating networks, EED of buildings, pinch analysis and process optimisation, David will further pursue his ambitions to reduce industries energy demand.