Sulsim® 6

Reaction Furnace

Empirical Kinetic Furnace Simulation

The reaction furnace of Sulsim® 6 has been substantially enhanced to allow greater access to Sulphur Experts’ industry recognized empirical plant test database. An extensive recompilation of the database from the past ten years (more than 500 plant tests) has produced the most comprehensive reaction furnace empirical model available.

All of the empirical kinetic models generate data on the thermal sulphur conversion efficiency, and formation of minor species such as COS, CS2, H2 and CO. The new empirical simulations include specific and distinct modelling of the following plant configurations:

  • standard acid gas feed configurations

  • oxygen-enrichment configurations (with empirical data from plants using 25 to 75+% oxygen)

  • ammonia burning configurations (both front-side split and straight-through configurations)

  • lean feed split-flow configurations

All of the simulation models can also be completely customized by the user with respect to the furnace production of H2, CO, COS and CS2. This feature provides for the most flexible empirical reaction furnace modelling available.

 Reaction Furnace Thermodynamic Model with Quench Section

Sulsim® 6 continues to support the traditional adiabatic thermodynamic reaction furnace model. In addition, Sulsim® 6 also allows the user to modify specific furnace reaction products by specifying a specific and independent "quench" temperature for H2, CO and the Claus reaction. This provides for a complex and flexible user modified thermodynamic equilibrium calculation.

Other Reaction Furnace Features

Sulsim® 6 continues to support the measured known outlet composition, furnace option which allows input of a measured furnace outlet composition. This is especially useful where the furnace composition is known with some degree of confidence.

Sulsim® 6 now allows for multiple furnaces in parallel or series as well as an option to configure a plant without a thermal reaction furnace at all.

Catalytic Converters

Sulsim® 6 utilizes a sophisticated, isenthalpic, free-energy minimization method for modeling the Claus reactions in the traditional catalytic converter. These routines have been specifically customized to recognize that many typical Claus plant components (H2, CO) do not react in the Claus reactor. The converter simulation is based on the converter inlet materials, inlet temperature and pressure and these calculations yield the expected converter outlet temperature and equilibrium composition.

The normal simulation of the Claus reaction in the catalytic converter is based on thermodynamic equilibrium. However, specification of the degree of approach to this level of conversion is permitted, thereby allowing simulation of deactivated catalyst beds. Independent kinetic limitation of the H2S:SO2 reaction, COS hydrolysis and CS2 hydrolysis is available for all of the converters. Sulphur dewpoint temperatures are calculated for both the converter inlet and outlet streams.

For Sulsim® 6, an all new empirical COS and CS2 reaction model has been developed to provide for accurate simulation of the extent of these important reactions. This model is also based on our extensive plant testing database and represents a significant breakthrough in modeling of Claus reactors.

The model also allows for user specified deactivation of the Claus reactor with respect to the COS and CS2 reactions and the new empirical model will respond accordingly to that information.

New optimization routines in Sulsim® 6 allow for convergence of any Claus converter to a specified outlet sulphur dewpoint margin. This allows the user to optimize the converters automatically with each execution without manual iteration on the upstream reheater operation.

Sulsim®6 also allows for rigorous modeling of several non-traditional catalytic processes and configurations including:

  • selective oxidation reactors

  • sub-dewpoint reactors

The selective oxidation bed allows H2S to react directly with oxygen to form sulphur. The conversion of H2S and its yield to sulphur are user-specified and the program calculates the bed outlet temperature and composition and the sulphur production rate.

The sub-dewpoint reactor completes the Claus reactions below the sulphur dewpoint temperature in order to improve the extent of reaction. The sulphur which is produced from this reaction will accumulate in the reactor to give the user an accurate measure of sulphur accumulation rates in the unit, which is useful in determining optimum cycle times on these processes.

 

Wasteheat Exchangers

The traditional modeling of wasteheat exchangers called for heat exchange calculations only. However, recent investigations into the operation of these units have indicated that these units can have significant additional reaction of certain components. For the first time ever, Sulsim® 6 has incorporated a comprehensive empirical model for simulating the reaction of several components (including H2, CO, COS and H2S) in the wasteheat exchanger. This allows for accurate modeling of the process stream composition through the wasteheat exchanger. The user has the option of using this empirical model or operating the exchanger in the traditional non-reactive mode. Both single and double pass wasteheat exchangers are permitted, enabling specification of a hot-gas bypass-type reheater if desired.

Condensers

All sulphur equilibration and dewpoint calculations are carried out by the free-energy-minimization technique to obtain the proper composition of sulphur vapour (S1 to S8). For condensers, the liquid sulphur is removed as the product stream, assuming there is no sulphur mist or fog entrainment. Provision for specification of liquid sulphur entrainment as a percentage of sulphur production is incorporated. The sulphur product stream temperature is assumed to be the same as the condenser outlet gas stream.

Reheaters

Provisions for the following types of reheaters are incorporated within Sulsim® 6.

  • hot-gas bypass (from wasteheat exchanger)

  • direct-fired in-line burners (fuel or acid gas)

  • indirect reheaters (steam, indirect fired reheater)

  • gas-gas heat exchangers (process gas on both sides)

The hot-gas bypass fractions are calculated by enthalpy balances. For this purpose, it is assumed that the bypass stream has the same composition as the wasteheat exchanger effluent. Sulphur vapour composition variations are accommodated in the calculation.

For direct-fired burners, the calculated burner fuel/acid gas and air flow rates are those required to achieve the specified converter inlet temperature. Provisions for artificially changing the burn stoichiometry or for independently specifying the fuel/acid gas and air flow rates to each of these burners is also included.

Indirect reheaters calculate the necessary heat duty to raise the process gas to the specified inlet temperature. Gas-gas exchangers allow the user to specify which process stream will be used to provide the necessary heat duty, and calculate the temperature change in that stream.

 

Reheaters

Provisions for the following types of reheaters are incorporated within Sulsim® 6.

  • hot-gas bypass (from wasteheat exchanger)

  • direct-fired in-line burners (fuel or acid gas)

  • indirect reheaters (steam, indirect fired reheater)

  • gas-gas heat exchangers (process gas on both sides)

The hot-gas bypass fractions are calculated by enthalpy balances. For this purpose, it is assumed that the bypass stream has the same composition as the wasteheat exchanger effluent. Sulphur vapour composition variations are accommodated in the calculation.

For direct-fired burners, the calculated burner fuel/acid gas and air flow rates are those required to achieve the specified converter inlet temperature. Provisions for artificially changing the burn stoichiometry or for independently specifying the fuel/acid gas and air flow rates to each of these burners is also included.

Indirect reheaters calculate the necessary heat duty to raise the process gas to the specified inlet temperature. Gas-gas exchangers allow the user to specify which process stream will be used to provide the necessary heat duty, and calculate the temperature change in that stream.

Tail Gas Analyser and Combustion Air Specification

Sulsim® 6 incorporates a new methodology for determining the combustion air flow rate to the reaction furnace which allows for considerable flexibility in modeling the entire plant. The primary method for setting the combustion air flow rate is through the specification of the new Tail Gas Analyser. This unit is placed at a user specified location in the plant downstream of the reaction furnace and will determine the correct air flow based on the user specified air demand condition. The furnace model also allows for direct user specification of the total air flow to the reaction which will over-ride the requirement for a tail gas analyzer and air flow controller.

Tail Gas Clean-up Processes

Sulsim® 6 allows for modeling of most of the popular tail gas clean-up processes and incorporates modeling of all of the main process unit operations:

  • reducing gas generator (tail gas burner or reheater)

  • hydrogenation reactor

  • quench tower

  • amine absorber and regenerator or

  • liquid redox type H2S absorber / reactor

The reducing gas generator uses free energy minimization calculations and user specified temperatures and pressures to calculate outlet composition and fuel/air flow rates. The hydrogenation/hydrolysis bed also uses free energy minimization calculations to determine the bed outlet composition and temperature. The hydrogenation/hydrolysis bed outlet stream can then be fed to a cooler and water quench tower where liquid water can be removed from the process.

In the amine absorption material balance unit, the recycle acid gas and absorber overhead stream compositions are calculated based on the user specified absorber overhead H2S content and the recycle acid gas CO2 content. In the liquid redox material balance unit, the product sulphur stream and the vent gas streams are calculated based on the user specified vent gas H2S content.

Incinerator / Oxidizer

Sulsim® 6 offers two options for tail gas incineration.

  • thermal incinerator/oxidizer

  • catalytic incinerator/oxidizer

Both options allow specification of the stack oxygen content while the thermal incinerator outlet temperature and the catalytic incinerator inlet temperature are also specified. The program determines the fuel and air flow rates which are consistent with these variables as well as the stack composition.

Sulsim® 6 also allows the user to specify an operating condition with incomplete combustion in the incinerator. In this case the user specifies the extent to which individual components will break through as a residual in the incinerator effluent.

Additional Units

Sulsim® 6 includes the following additional unit operations:

  • acid gas preheaters

  • temperature and pressure gradients

Preheaters allow for preheating of acid gas and air streams to the reaction furnace. Gradient units provide heat and material balance calculations to stimulate specified heat losses and pressure drops.