Process Engineer Assessment

Scenario: Modular Nitric Acid Plant

Process Engineer Assessment 

You are tasked with designing a modular NO₂ absorption system suitable for converting nitrogen dioxide to nitric acid. The system must be designed for containerised deployment alongside upstream and downstream modules. 

Your Goal: 

Develop a conceptual design for the absorption system only, sized and structured to fit within a modular deployment strategy (e.g. a shipping container), with a build time frame of approximately 3 months. 

System Parameters 

  • Feed gas composition: 10% v/v NO₂ in air 

  • Flow rate: 5,000 SLPM (at 0 °C, 1 atm) 

  • Gas temperature at inlet: 50 °C 

  • Pressure: Atmospheric 

  • Ambient conditions: Outdoor installation (–5 to 40 °C) 

  • Space constraint: Standard 40-foot shipping container (note: this container will also house other equipment, so plan for efficient spatial use) 

  • Design intent: The system should be modular for ease of transport, scalability, and maintenance. 

Available Utilities 

You may assume the following utility specifications: 

  • Cooling water: 25 °C inlet, 3 bar supply pressure 

  • Compressed air: 6 bar gauge, filtered 

  • Power: 415 V, 3-phase 

  • Instrumentation power: 24 V DC available 

  • Drainage: Gravity-fed access with limited holding volume 

Design Calculations 

  • Include an estimation of the maximum achievable nitric acid concentration under atmospheric pressure based on your selected absorption method and design assumptions. 

Deliverables 

Please submit a multi-page PDF containing the following: 

1. Process Flow Diagram (PFD) 

  • A digitally illustrated process flow diagram of the absorption system. 

  • Annotate modular design features, key process steps, and assumptions clearly. 

  • You may use any digital tool you’re comfortable with (e.g. Visio, Lucidchart, AutoCAD, etc.). 

  • A simplified mechanical layout overlay is optional but welcome. 

2. Design Calculations 

Include clear, legible calculations (typed or hand-written and scanned) covering: 

  • Material balance 

  • Gas pressure drop 

  • Absorption column sizing based on: 

  • Overall mass transfer coefficient 

  • Number of transfer units (NTU) 

  • Height of a transfer unit (HTU) 

  • Effective packing surface area 

  • Operating and equilibrium lines 

  • Solvent selection and flow rate 

  • Any other calculations you consider relevant 

3. Design Specification Sheet 

Summarise the key parameters of your proposed system, including: 

  • Absorber type (e.g. packed bed, spray tower, etc.) and rationale 

  • Estimated column dimensions and packing characteristics 

  • Solvent type and flow rate 

  • Expected efficiency/conversion 

  • Key integration considerations (e.g. drainage, maintenance, redundancy, startup/shutdown) 

4. Optional: Commentary and Engineering Judgement 

If you wish, include a short section (~half page) with your observations or design rationale, such as: 

  • Alternative designs you considered 

  • Risks, bottlenecks, or integration concerns 

  • Assumptions you had to make due to lack of data 

  • Opportunities for future improvement or scale-up 

This is not mandatory but helps demonstrate system-level thinking and your ability to evaluate trade-offs. 

Submission Instructions 

  • Email all files to careers@plasmaleap.com and use subject line: Process Engineer Assessment – [Your Name] 

  • Submit within 48h of receiving this test 

  • Please do not exceed the time limits unless otherwise agreed