Clemente Pedro Nunes

A Cost-Based Strategy to Design Multiple Shell and Tube Heat Exchangers

Process Integration has been applied in several industrial processes mainly using standard shell and tube heat exchangers (1-1 or 1-2). The flow arrangement in 1-2 multiple shell and tube heat exchangers involves part counter-current flow and part co-current flow. This fact is accounted for in the design by introducing a F T correction factor into the 1-1 heat exchanger design equation. To avoid some steep regions in the feasible space of heat exchangers design some authors introduce other parameters like Xp or G. Until now it was not possible to have an overall map to give some guidelines of how to choose between the several Xp approaches established in the literature. This paper summarizes the current existing criteria in a general design algorithm (DeAl 12 ) to show a path for the calculations of the main design variables of the heat exchanger. Also a new strategy design algorithm (StratDeAl 12 ) is introduced in this paper to allow the best choice between the existing Xp approaches based on the heat exchanger cost minimisation. Several examples illustrate the advantage of using the developed algorithm and the deviations obtained in the heat exchanger cost if a wrong approach was chosen.

Logistics cost analysis of rice residues for second generation bioenergy production in Ghana.

This study explores the techno-economic potential of rice residues as a bioenergy resource to meet Ghanas energy demands. Major rice growing regions of Ghana have 70-90% of residues available for bioenergy production. To ensure cost-effective biomass logistics, a thorough cost analysis was made for two bioenergy routes. Logistics costs for a 5 MWe straw combustion plant were 39.01, 47.52 and 47.89 USD/t for Northern, Ashanti and Volta regions respectively. Logistics cost for a 0.25 MWe husk gasification plant (with roundtrip distance 10 km) was 2.64 USD/t in all regions. Capital cost (66-72%) contributes significantly to total logistics costs of straw, however for husk logistics, staff (40%) and operation and maintenance costs (46%) dominate. Baling is the major processing logistic cost for straw, contributing to 46-48% of total costs. Scale of straw unit does not have a large impact on logistic costs. Transport distance of husks has considerable impact on logistic costs.

Process integration of a dynamic industrial system

Abstract The aim of this study is to obtain a dynamic modelling and simulation of a Portuguese industrial integrated system composed of three different processes. This work includes the analysis of the optimal integration of the different units, and the study of the effect of some operational and atmospheric conditions on the system to maximize its global thermal efficiency. The cogeneration system was modelled and analysed using the GateCycle 5.34.0.r software. It was concluded that the electric and the thermal power obtained strongly depend on air and economizer cooling water temperatures. The whole integrated process (cogeneration, plate exchangers and salt production unit) is simulated and exploited through gPROMS 2.1.1 . The best start-up conditions were established. The minimum number of ponds required strongly depends on atmospheric conditions, but it can never be less than three in order to obey the operational defined temperature intervals. The scheduling of the evaporation ponds to be put into operation is also investigated in order to enhance the salt production and to optimise the salt harvesting. The simulation indicates that it is better to have the minimum number of ponds working (higher temperatures inside the ponds) and to have a “turbo” pond that receives a larger quantity of heated brine than the others. It was also studied the effect of different atmospheric conditions, and the number of ponds in service required to overcome the more adverse atmospheric conditions. The global process efficiency (thermal and electric power over natural gas consumption) is approximately 92%. However, the effective global thermal efficiency of the whole integrated site (accounting for the existing losses into the open air of the evaporation process) is in the range of 75– 80%, depending on the atmospheric and operational conditions considered.

AquoMin: Targeting and design of mass-exchange networks featuring regeneration recycle

Abstract This study addresses the design of Mass Exchange Networks (MEN) featuring regeneration recycle. AquoMin is a friendly-user software based on Pinch Analysis and Mathematical Programming. It has been improved to include a new module dealing with the regeneration recycle strategy. A general algorithm was built to obtain the tergets of this strategy. An Example Problem is used to evaluate the results of the different strategies that can be employed to minimise water and wastewater flowrates. A trade-off between regeneration flowrate and concentration was achieved for the present strategy, leading to a regeneration flowrate reduction of 16% and an increase of 17% in inlet concentration of the regeneration process

Aquomin: An approach to pollution prevention based on pinch analysis

Abstract This paper presents the most recent version of the software AquoMin that is a wastewater minimisation analysis tool. It involves a link to GAMS to help with the design of Mass Exchange Networks (MEN) featuring regeneration re-use. More specifically, a Non Linear Problem (NLP) was developed to determine the most important design parameters. Both the software and proposed design method are illustrated by means of a case study.

Retrofit design of hydrogen distribution systems: a practical case study

Abstract The recent environmental restrictions to cut down pollutant gas emissions, along with the increasing drive to process heavy and sour crude oils, and the refining market trends toward gasoline and middle distillate fuels, have led to increased hydrogen demands associated with hydrotreating and hydrocracking processes. This manuscript addresses the synthesis of optimal hydrogen distribution systems bearing in mind both economic and operational issues. The optimal flowsheet configuration is established following a deterministic optimisation approach. One practical case study is provided to highlight the importance of an effective hydrogen management strategy amongst other production planning and scheduling decisions. This work was carried out within an industrial research project in close collaboration with Galp Energia and it is focused on a Petrogal’s refinery located near Sines, Portugal.

H2TT – A pinch analysis software tool for refinery hydrogen network management

Abstract Hydrogen management practices in the petroleum industry aim at maximising refining gross margins while addressing environmental and production planning issues. A novel pinch analysis software tool – H2TT – establishes targets for the minimum hydrogen utility consumption prior to detailed network design. H2TT is an interactive spreadsheet-based software programmed in Visual Basic for Applications that analyses the potential for reusing hydrogen across the refinery based on pinch analysis principles. This software identifies the existence of bottlenecks in the hydrogen distribution system and gives valuable insights into the appropriate placement of additional purification units within the hydrogen network. Moreover, it can be used to assess the availability of hydrogen at different purity levels. One example is provided to illustrate the applicability of H2TT for the integration hydrogen resources in refineries and petrochemical plants. This work was carried out within an industrial research project in close collaboration with Galp Energia and is focused on a Petrogal refinery located near Sines, Portugal.

Influence of brine spray system on the thermal salt recrystallisation process by dynamic simulation

Abstract A distributed dynamic model was built using gPROMS 2.3.7 language for an integrated Process including a cogeneration system, a plate heat exchangers set and a salt recrystallization process. It was analyzed the effect of a simulated spray system model on the integrated process, by comparing the global performance of the system with and without sprays. Due to air drift issues, quasi-random time daily profiles for the allowed operation of the spray system (on-off working time periods) were created. Using three distinctive atmospheric scenarios, several ponds spray distributions schemes were analysed. A sensibility analysis of the salt production was considered by changing the brine flow rate fraction entering in the ponds through taps and by sprays.