Project Synopsis

Design services for a sodium  hydrosulfide (NaHS) production area of a greenfield antimony refining facility. Simulation Diagram

Project Summary


The client, an antimony mining concern, contracted with Process Engineering Associates, LLC (PROCESS) to provide process design services for a sodium  hydrosulfide (NaHS) production area of a greenfield antimony refining facility.  This work was performed subsequent to the feasibility-level process design work PROCESS completed under a previous project. Specifically, PROCESS completed the following design tasks for this project:

  • Task 1 – NaHS reactor technologies alternatives evaluation
  • Task 2 – Process design basis preparation
  • Task 3 – Computer process simulation and process flow diagram preparation
  • Task 4 – Detailed and equipment duty specifications preparation

Prior to initiation of design work, PROCESS was tasked with identifying, technically screening, and evaluating technologies for the NaHS reactor.  A multi-stage contactor/separator system manufactured by a company specializing in NaHS production systems was selected for the reactor technology.  The design basis preparation involved updating the design basis information generated during the previous project as well as determining inlet gas stream H2S concentrations for the minimum, average, and maximum design cases.  Once the design basis was completed, PROCESS executed detailed computer process simulations for the NaHS production system and generated comprehensive process flow diagrams using licensed commercial process simulation software.  Unit operations simulated included:

  • Inlet gas cooler
  • Inlet gas HCI absorber
  • NaHS reaction system (contactor/separator)
  • Recycle NaHS cooler
  • Outlet tail gas scrubber
  • Storage tank vent gas scrubber

A detailed equipment specification was prepared for a NaHS reaction system skid that included the reactor/separator, recycle NaHS cooler, NaHS product pump, and all associated process controls.  This specification was used to obtain a final capital cost estimate from the selected NaHS reaction system manufacturer.  In addition, duty specifications were prepared by PROCESS for the system ancillary towers (HCI absorber, tail gas scrubber, and vent gas scrubber) that were to be fabricated by local contractors.

The simulation and design of the NaHS reaction system was especially challenging due to the small operating envelope that was dictated by the design basis.  Multiple simulation runs were required to optimize the number of contacting stages, and NaHS recycle rate and temperature such that the NaHS product concentration, product Na2S contamination level, and offgas H2S concentration all met the design basis requirements.

Industry Type

  • Minerals & Metals Refining

Utilized Skills

  • Alternatives technical screening
  • Computer process simulation
  • Multi-stage reactor design
  • Scrubber design
  • Design optimization
  • Detailed equipment specification preparation
  • Front end engineering design (FEED)
  • Waste minimization process design

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