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Duty Definition and Equipment Specification (DuDES)

1. Purpose

Duty Definition and Equipment Specification (DuDES) is a methodology to help process technologists select appropriate equipment based on the process understanding gained from using Britest tools. It can be used when selecting equipment for:

  • New capital investment, or
  • Siting processes in existing assets

DuDES is used by a process development team to draw up the duties and specifications for the equipment needed to carry out a task on a Process Definition Diagram. Where information gaps exist, these are clearly identified, and actions are devised to collect essential information.

The equipment specifications generated using DuDES are appropriate to both process characteristics and business needs.

DuDES

  • Facilitates equipment specification based on process understanding
  • Identifies further information needs for detailed equipment design.
Britest Duty Definition and Equipment Selection Poster
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2. Information requirements

Essential information for applying DuDES Useful information to include in DuDES 

Initial Screening Analysis

Process Definition Diagram of process concept

Qualitative duties for each process task

Transformation Map

Driving Force Analysis

Throughputs of key process materials

Mass balance for whole process

Quantitative duties for each process task
Some knowledge of equipment capabilities

3. Methodology

1. Understand the process in terms of fundamental physics and chemistry

Identify fundamental technical needs

Identify key business drivers

  • Initial Screening Analysis and PrISM
2. Devise a process concept
  • Use Transformation Map, Rich Pictures and Cartoons, and DFA to develop process concepts
  • Draw PDDs to represent the options generated
  • Consider carrying out mass and energy balances
3. Define what the process needs the equipment to deliver using the DuDES checklist and table
  • Carry out an initial screen for continuous processing opportunities
  • Perform a quick assessment of each PDD task, identifying equipment needs and knowledge gaps using the DuDES checklist and table.
    • Input from both chemists and engineers is required to capture all necessary specifications
    • Identify actions to address knowledge gaps
  • Check whether equipment exists to meet the needs
  • Consider splitting and combining tasks on the PDD when mapping to equipment items
  • Create a prioritised action list to find information for a full equipment specification
4. Collect the necessary information to complete equipment selection, and review

Complete actions identified in step 3.

 

Review the required process tasks

  • Use the revised PDD of the process concept
  • You will already have considered whether to split or combine tasks

Update the task duties on the DuDES table

  • Qualitatively (revise if necessary)
  • Quantitatively (figures from calculations)
5. Complete equipment selection and detailed design using standard chemical engineering methods

 

3.1 DuDES table

PDD task Musts and Desirables including comments

Avoids and Prefer Nots including comments

 Data needed and actions, including comments
Task Purpose


Mass Balance


Residence time


Mixing


Heat Transfer


Mass Transfer


Phases


Flow Characteristics


Physical Processing


Operability


Other



 

Use the DuDES checklist for additional specifications that may need to be considered.

3.2 Screening for continuous processing opportunities

Consider continuous processing when the process has any of the following features:

  • The intrinsic chemical rate is fast (seconds or minutes)
  • The reaction is mixing sensitive
  • The product or intermediates are short-lived
  • The reaction is heat- or mass-transfer limited (heat and mass transfer can be intensified)
  • The hazards are large, so a small inventory is advantageous (intrinsic safety)

3.3 Equipment screening

Follow-up any qualitative DuDES table entries by estimating quantitative duties using shortcut calculations. Then check equipment exists to meet the requirements

  • e.g. heat transfer per unit volume, UA/V

Consider generic classes of equipment, not specific equipment models. If no equipment can be found to meet the process needs, then revisit the process concept and iterate

  • e.g. if the required UA/V for exothermic reaction is too high for available equipment designs, then redesign the process concept to reduce heat transfer requirement, using dilution, multiple injections of second reactant etc.

3.4 Splitting and combining process tasks

In some cases, a better process will result from combining two or more tasks on a PDD in a single item of equipment. In other cases, an advantage can be obtained by splitting a single task into two or more items of equipment. The following table indicates when combining or splitting tasks should be considered:

When to consider splitting tasks across multiple pieces of equipment When to consider combining tasks within a single piece of equipment

The process needs or duties vary significantly as the task progresses

Process needs or duties may include:

  • Heat transfer intensity – the heat transfer capability needed to remove reaction heat
  • Mass transfer intensity
  • Mixing requirement

E.g. A second order exothermic reaction where the peak heat output occurs in the first 5-10% of the reactor volume

  • Sizing the whole reactor for the peak heat load could result in excessive cost
  • Consider an intensive device sized for the initial peak output coupled to a less intensive device for the remainder of the reaction

 All these criteria should be met:

  1. The materials present in all of the tasks to be combined should be compatible with each other,
  2. The required processing conditions should be similar, and
  3. The duties required of the equipment should be similar

If the duties or processing conditions for the tasks being combined are too dissimilar, the resulting compromises lead to a higher overall cost


 

 

Supporting documents

DuDES Checklist

Page last updated 4th January 2016
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