Project Synopsis

Evaluate the performance of an existing nitrogen oxides (NOx) scrubbing system to improve operability, reduce maintenance problems, and help prevent emissions excursions.

Project Summary


The client owns and operates and specialty catalyst manufacturing facility.  The client contracted Process Engineering Associates, LLC (PROCESS) to evaluate the performance of an existing nitrogen oxides (NOx) scrubbing system.  The system includes a packed bed scrubber, gas pre-heater, selective catalytic reduction (SCR) unit, and an ammonia scrubber.  The evaluation involved a detailed review of the packed bed scrubber for removal of nitrogen dioxide (NO2). The packed bed scrubber was designed to remove NO2 from the catalyst oven offgas using a 50% sodium hydroxide (NaOH) and 15% sodium sulfite (Na2SO3) scrubbing solution.  The exhaust from the packed bed scrubber is combined with other process offgases and fed to the downstream SCR.  Process data had indicated that current operation of the packed bed scrubber was not in alignment with specified performance criteria. Project tasks included:

  • Process evaluation basis development
  • Regulatory evaluation basis development
  • Computer process simulation and process description preparation
  • Systems operational evaluation
  • Development of recommendations to improve system performance.

PROCESS evaluated the operation of the scrubber in two areas.  First, a heat and mass balance (HMB) was performed around the system to simulate existing operations and define the process operating conditions necessary to optimize NO2 removal efficiency.  The existing process was modeled using PROCESS’ licensed commercial simulation software to produce a mass and energy balance at peak loading conditions.  During the course of the project, it was determined through scrubber testing that the actual peak inlet NOx loading to the scrubber was 25 -30% higher than the design maximum loading case.  Therefore, the review included the original design maximum conditions as well as a new peak loading condition.  Second, the physical design of the system was evaluated to provide recommendations on potential equipment configuration changes, operational modifications, and maintenance procedures that could be implemented to help improve operation of the scrubber.  This portion of the evaluation included a detailed review of the scrubber physical parameters such as packed bed diameter and height, packing size, liquid flow rate, gas velocity, system pressure drop, chemical reagent pump sizing and control loop configurations, and system blow down design.   As a result of the evaluation a series of recommendations were presented to the client to improve the performance of the system.  Major recommendations included:

  • Increase the scrubber blow down rate to decrease total dissolved solids and increase the scrubber efficiency
  • Perform site-specific tests to determine the optimum scrubber sodium sulfite dosage rate for the purpose of further improving on the scrubber removal efficiency
  • Implement calibration and maintenance procedures for critical scrubber system instrumentation
  • Revise the system operating permit to include overall NOx removal requirements (rather than the current scrubber-specific NOx removal requirements).

Industry Type

  • Industrial Materials Manufacturing

Utilized Skills

  • Regulatory compliance
  • Process troubleshooting
  • Process optimization
  • Emissions control equipment optimization

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