Amir Hossein Tarighaleslami

Optimisation of non-isothermal utilities using the Unified Total Site Heat Integration method

Total Site Heat Integration is an effective method for design of large scale utility systems that serve large chemical processes, such as refineries, petrochemicals or even lower temperature chemical and process plants. Total Site Heat Integration of different chemical plants might confront batch, semi-continuous or continuous plants which are clustered into one large site. Excess heat produced from one plant could be transferred to other plants using an intermediate fluid. In this paper, Total Site optimisation of targeting utility generation and consumption for lower temperature processes, which mainly use non-isothermal utilities, is presented. The utility temperature selection optimisation applies to the recently developed Unified Total Site Heat Integration Targeting (UTST) method. The new method shows that, for low temperature processes where non-isothermal utilities are used, the supply and target temperatures of a utility is an important constraint, while for higher temperature processes, where isothermal utilities are applied, no significant change in targets from conventional Total Site are obtained. New heuristics based on UTST method with respect to non-isothermal utility temperature selection are proposed. A Kraft Pulp Mill case study has been investigated in this research, using optimised non-isothermal utilities, showing a 3.6 MW increase in heat recovery, 0.87 MW decrease in shaft work generation, and

Heat Transfer Enhancement in Heat Recovery Loops Using Nanofluids as the Intermediate Fluid

330,000 /y utility cost saving in the system applying the new UTST method compared to the conventional Total Site method.

A comparison of utility heat exchanger network synthesis for total site heat integration methods

In this paper, the effect of replacing water with various nanofluids as the heat transfer media in an industrial Heat Recovery Loop (HRL) have been modelled. Generally, nanofluids are prepared by distributing a nanoparticle through a base fluid such as water. Suspended nanoparticles slightly affect the thermal and physical properties of the base fluid. Primarily nanoparticles are added to improve the fluid’s heat transfer characteristics by increasing its Reynolds number and thermal conductivity. Results show that by applying various HRL design methods and a nanofluid as an intermediate fluid, an increase in heat recovery is possible without the need for extra heat exchanger area and infrastructure. With the addition of 1.5 vol.% CuO nanoparticles to the HRL fluid using constant temperature storage method, heat recovery from liquid-liquid heat exchangers increases between 5 % and 9 %. In the case of air-liquid exchangers, the air-side heat transfer coefficient limits the impact of using a nanofluid. In other cases, the duty available from the process stream, such as a condenser, significantly restricts the heat transfer benefit of using a nanofluid. Alternative to increasing heat recovery, results show that applying a nanofluid in the HRL design phase enables heat exchanger area to decrease significantly for liquid-liquid matches.

Assisted heat transfer and shaft work targets for increased total site heat integration

This paper compares Utility Heat Exchanger Network (UEN) design between two Total Site Heat Integration (TSHI) methods, the Conventional Total Site Targeting method (CTST) and the recently developed Unified Total Site Targeting (UTST) method. A large Kraft Pulp Mill plant has been chosen as a case study. Total Site targets have been calculated using a ExcelTM targeting spreadsheet and networks have been designed with the help of SupertagetTM for both the CTST and UTST methods. To achieve heat recovery and utility targets, both series and parallel utility heat exchanger matches for non-isothermal utilities are allowed in the CTST method, while series matches are allowed in the UTST method if the heat exchangers in series are from the same process. Series matches based on CTST method may create a dependency on two or more separate processes, which operational and control issues may occur, higher piping costs may be imposed, and utility target temperatures may not be achieved in the consecutive processes if one or more processes were to be out of service. Relaxation of the network can resolve these issues for the CTST method; however, if the relaxation occurs on the side of the utility loop that constrains heat recovery, the net heat recovery targets may not be achieved within the Total Site. The UTST method with its modified targeting procedure may offer slightly lower heat recovery targets but with simpler UEN design compared to CTST method are more realistic and achievable. Finally, after UEN design, non-isothermal utility loops need to be balanced in terms of mass and energy for both methods.

Impact of Hybrid Heat Transfer Enhancement Techniques in Shell and Tube Heat Exchanger Design

Total Site Heat Integration (TSHI) provides a valuable framework for practical integration of multiple energy users. Previous studies have introduced the idea of utilising process heat recovery pockets to assist TSHI. However, these methods are shown to be effective for only some Total Site (TS) problems. As a result, this paper presents a new method for calculating assisted heat transfer and shaft work targets for an example TS problem. Analysis results show that assisted heat transfer increases TSHI only when a process heat recovery pocket spans the TS Pinch Region. The maximum assisted TSHI can be targeted by comparing each heat recovery pocket to the Site Utility Grand Composite Curve (SUGCC) using background/foreground analysis. Where heat recovery pockets span two steam pressure levels away from the TS Pinch Region (usually above), the example shows the potential for assisted shaft work production. In this case, the source segment of the heat recovery pocket generates steam (e.g. MPS), which replaces steam that would otherwise have been extracted from a steam turbine. The sink segment of the heat recovery pocket consumes lower pressure steam (e.g. LPS), which is extracted from the turbine. If a heat recovery pocket falls outside these two situations (assuming direct inter - process integration is disallowed), the entire pocket should be recovered internal to a process.

Integration options for solar thermal with low temperature industrial heat recovery loops

Despite the advantages of shell and tube heat exchangers, one of their major problems is low thermal efficiency. This problem can be improved by using heat transfer enhancement techniques such as adding nanoparticles to the hot or cold fluids, and/or using tube inserts as turbulators on tube side as well as changing baffles to a helical or twisted profile on the shell side. Although all of these techniques increase the thermal efficiency; however, engineers still need a quantitative approach to assess the impact of these technologies on the shell and tube heat exchangers. This study attempts to provide a combination of such techniques to increase the impact of these improvements quantitatively. For this purpose, at first stage the thermal and hydraulic characteristics of pure fluid, Al2O3/water nanofluid in a plain tube equipped with and without twisted tape turbulator is evaluated based on a developed rapid design algorithm. Therefore, the impact of using enhanced techniques either in form of individual or in hybrid format and the increase of nanoparticle concentration in base fluid have been studied. The results show that using turbulators individually and in hybrid format with nanofluid can be effected on design parameters of a typical heat exchanger by reducing the required heat transfer area up to 10 %.