Improving the assessment of process reagent plants and utilities for high temperature hydrometallurgical process plant during early stage project development

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The current approach taken during the early stages of project development for high temperature hydrometallurgical plants (HTHPs) does not allow time for evaluating process reagent plants or adequately assessing the potential to recover low grade waste heat (LGWH). Therefore, there is a greater risk of making sub-optimal decisions when selecting process reagent plant technology and integrating LGWH recovery into the overall facility design. These decisions have a detrimental impact on energy efficiency and economic outcomes. The primary reason for the lack of integration of process reagents plants – and the related assessment of LGWH available for recovery – lies in the absence of a modified gated project development methodology, including the necessary models, to allow for better decision making in the early stages of project development. A modified project development process has been developed for use from the Scoping Study (FEL-1) stage to Front End Engineering Design (FEL-3). This methodology will allow project design engineers to independently and efficiently – using minimal effort – evaluate and rank process reagent technologies by plant type and also by combination, for a given set of technical and financial parameters. The methodology includes the use of empirical models for hydrometallurgical plant and process reagent plant prediction, which have been developed based on actual plant design data. The models can cater for different hydrometallurgical plant scopes and a range of plant capacities. The evaluation was undertaken using a purpose-designed, integrated technical and financial model. Case studies based on a nickel laterite flowsheet were developed to demonstrate the evaluation process; the ultimate objective was to select and rank the combinations of process reagent plant technologies. The evaluation also identified how changes in major operating cost inputs affected technology selection. The benefits of applying the developed methodology during Pre-feasibility Study Level (FEL-2) include earlier selection of process reagent plant technology and specification for Front End Engineering Design (FEL-3). As a result, more definitive information is provided for procurement activities. Additionally, this approach produces an integrated overall plant facility design, maximising the project’s economic value and minimising future evaluation effort and potential re-work. The key outcomes from the research were: • At FEL-2 stage, it is important to prioritise the selection of technology for – in order of priority – the sulphuric acid plant, ammonium sulphate plant, hydrogen sulphide plant, air separation plant and hydrogen plant. This improves technical decision-making and, commensurately, maximises the accuracy of input data for the cost estimate and financial evaluation. • The decision about technology selection is most important for the sulphuric acid plant, particularly with respect to deciding whether to select low pressure (LP) steam generation technologies. These decisions overwhelmingly influence the energy balance of the integrated plant and the combined process reagents plants’ capital, operating costs and net present value (NPV). The NPV of all potential combinations of process reagent technology, which include the two highest ranked sulphuric acid plant technologies, lies within 5% of the NPV of the highest ranked technology combination. This compares with between 6% and 15% for the remaining combinations, including the third- to sixth-ranked sulphuric acid plant technologies. If the sulphuric acid plant technology is correctly selected, then the impact of the other technologies on the project economics at FEL-2 is relatively minor, with less impact on net present value (NPV). • Depending on the technology selected during FEL-2, this choice may have a material financial impact on the outcome of the study, when referenced to accepted industry evaluation standards. Across the 32 potential combinations of process reagent plant technologies investigated, the range of financial outcomes included USD94 million (42%) for capital costs, USD10 million (14%) for annual operating costs and USD118 million (15%) for NPV. The results of this research demonstrate the importance of evaluating alternative technology options, with the exception of the air separation plant technologies. • Variations in key operating cost parameters generally do not significantly change the ranking of the preferred technologies; however, they may change the ranking of the technology combinations. • Electric power generation of up to 50% of total plant load is potentially available using organic Rankine cycle LGWH recovery technology for the metals plant scope, with corresponding significant greenhouse gas emission reductions. • The methodology could be extended to include other material flows such as water, process flow sheets with similar characteristics, and the design and evaluation of suitable engineered multi-component systems. • The viability of the recovery of LGWH is improved when included in the early stages of design, as the options can be appropriately assessed in conjunction with the project facility’s electric power requirements.