Project Synopsis

Computer process operations simulation of two different NaHS sour gas sweetening units.

Project Summary


The client operates a design and manufacturing facility for the production of custom sodium hydrosulfide (NaHS) reaction systems and desired a better method for the development of the mass and energy balance information required to do reactor, product separator, heat exchanger, and pump detail process design.  To this end, the client contracted Process Engineering Associates, LLC (PROCESS) to develop a computer process simulation of the operation of two different NaHS sour gas sweetening units (a three-stage unit and a single-stage unit) for the ultimate client in this case, an independent petroleum refining company.

Tasks completed in support of the three-stage NaHS unit simulation included:

  • Developed a process simulation model and performed specific process simulations using licensed commercial process simulation software to determine: (1) the overall system mass and energy balance, (2) the heating/cooling duty for a recycle product heater/cooler, (3) the cooling duty for a sweet gas cooler, and (4) the effect of recycle product rate and temperature on acid gas  (H2S) conversion and NaHS production
  • Calculated: (1) the heat loss from a NaHS product storage tank and (2) the heat loss from non-insulated process piping
  • Prepared a report presenting PROCESS’ final work product including process flow diagrams and material and energy balances for both normal and maximum operating cases as well as the heating and cooling duties for the required heat exchangers.

Tasks completed in support of the single-stage NaHS unit simulation included:

  • Performed process simulations of a single-stage, packed column NaHS sour gas sweetening system using licensed commercial process simulation software to determine: (1) the diameter of the packed column, (2) the depth of packing required in the column, (3) the required caustic feed rate, (4) the required product recycle rate, (5) the NaHS product quality, and (6) the estimated pressure drop through the column packing.
  • Reported these results to the client via project report

Development of the three-stage NaHS unit process simulation was especially challenging.  The NaHS reactors are limited-contact devices to prevent the reaction of CO2 in the sour gas with the incoming NaOH.  As such, PROCESS had to simulate a non-equilibrium device using the equilibrium-based simulation software.  In addition, a complex electrolytes thermodynamics and chemistry model had to be developed for the simulations to accurately predict sour gas H2S removal, NaHS product concentration, byproduct Na2S formation, and dilution and reactions heat production.

Although the NaHS unit simulation model requires some additional work to allow for future modeling of different sour gas compositions and H2S removal efficiencies, PROCESS developed a simulation tool for the client that will allow for quicker and more accurate determination of the mass and energy balance information required for NaHS unit design.

Industry Type

  • Petroleum Refining

Utilized Skills

  • Computer process simulation
  • Simulation tools development
  • Simulation of non-equilibrium devices
  • Develop thermodynamic and chemistry models for complex electrolytes
  • Waste minimization process design

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