Written by: Jackson Udy, PE
Process Engineer at Process Engineering Associates, LLC
August 26, 2026
Many clients engage Process Engineering Associates (PROCESS) for support in designing new processes or expanding and improving existing operations. However, determining the appropriate level of process design for a given project is not always straightforward. This article explains the typical scope of each level of a Process Design Package (PDP), the information needed to develop those packages, when each design phase is most appropriate, and what project risks may remain at the conclusion of each phase.
What Is a Process Design Package?
Chemical process design can generally be divided into two phases: preliminary process design and detailed process design. These phases are commonly referred to as FEL-0 or FEL-1 for preliminary design, and FEL-2 or FEL-3 for detailed design. Detailed design packages may also be referred to as a Schedule A, Basic Engineering Package (BEP), or Front-End Engineering and Design (FEED) package.
Do I Need a Preliminary Design or a Detailed Design?
A Preliminary Process Design, such as FEL-0 or FEL-1, gives clients the opportunity to evaluate technical feasibility, compare potential options for achieving their processing objectives, and develop preliminary design information. This early evaluation allows the project team to make critical design changes while the cost and impact of those changes remain relatively low. Examples of situations where a preliminary process design may be appropriate include:
• A client has developed a new process in the lab and wants to scale up to a pilot plant.
• A chemical plant is considering adding a new production unit.
• An oil refinery wants to see if it can reconfigure some idled equipment.
These real-world scenarios are well suited for a preliminary PDP because this phase helps verify the physical and economic viability of a project before significant additional investment is made. Different processing schemes can be evaluated, and the most practical options can be identified in a cost-effective manner. Once process feasibility and a cost-effective configuration have been established, detailed process design can begin.
What Is Included in an FEL-0/1 Preliminary Process Design Package?
The major deliverables from a preliminary PDP typically include:
1. Heat and Material Balance (HMB) (also referred to as a Mass and Energy Balance) – This document quantitatively describes the mass and energy flows throughout the process. It is the foundation of any process design and is used in later phases to size equipment and estimate operating costs.
2. Process Flow Diagrams (PFDs) – PFDs provide a visual representation of process and energy flows through the plant, including major process equipment and energy streams.
3. Technical and Economic Alternatives Evaluations – this step provides a structured review of process options that have not yet been fully defined. Examples may include selecting specific technologies, such as separation or drying methods; evaluating opportunities for heat recovery; and comparing the advantages and disadvantages of various configurations, such as single-train versus multi-train operation. These options can be evaluated from both technical and economic perspectives to help ensure the process meets its processing objectives cost-effectively.
4. Major Equipment List – A list of major process equipment, including required throughputs and duties.
5. Preliminary Layout – A preliminary layout provides an initial view of the footprint required for the process.
6. Process Risk Assessment – A process risk assessment identifies and comments on areas of the process design that may present risks to project success.
The six deliverables listed above are standard components of an FEL-1 package. However, if the process requirements are not yet clearly defined, an FEL-0 study may be performed first. In general, an FEL-0 package includes only items 1, 2, and 4 above. An FEL-0 HMB may include some “black box” process steps where feasibility is assumed rather than fully evaluated. Process feeds may not yet be defined, and feed conditioning or product purification requirements may still be unknown. Even so, an FEL-0 study provides a qualitative process description through PFDs and some quantitative HMB information, although typically with significant assumptions that limit the ability to develop reliable operating or capital cost estimates.
Once these deliverables are completed, a rough order-of-magnitude capital cost estimate, typically ±50%, and an operating cost estimate can be developed. With these estimates in hand, the client can determine whether the project should proceed to the detailed design phase. Other deliverables may also be included in an FEL-1 package, such as a process description, utility requirement summary, estimated emissions summary and environmental assessment, or preliminary project schedule.
What Is Needed to Prepare an FEL-0/1 Design?
Typical requirements for an FEL-0/1 design include the following:
- Product specification, i.e., desired product strength and allowable impurities.
- Description of reaction chemistry; kinetics are not always required at this stage.
- Feed concentrations/purities
- Desired production rate.
PROCESS can help clients define these specifications as part of the project design basis. However, client engagement in developing and confirming these specifications is very important. Changes to these requirements during the detailed design phase typically result in additional engineering effort, cost, and schedule impact.
If the information listed above is not yet available, an FEL-0 design can still be performed. An FEL-0 design can help guide the client in selecting these specifications and defining the process for later design phases.
What Risks May Still Remain After Completing an FEL-0/1?
An FEL-1 design provides a basis for further detailed design, but significant unknowns often remain at this stage. These factors vary by project, but common process and project risks remaining after FEL-1 may include:
- Missing physical property data for specialty chemicals/products
- Unknown environmental permitting requirements
- Undefined scope of other engineering disciplines, such as civil and electrical engineering.
- Undefined material selection for piping and process equipment.
- Capital cost estimates are rough order of magnitude level (±50%).
A process risk assessment is often performed as part of the FEL-1 design package to document identified design risks. These items are then revisited in later engineering phases after a decision to proceed has been made. Additional discussion of minimizing process design risk can be found in a previous article here.
Am I Ready for Detailed Process Design?
Once an FEL-1 design is completed and a decision has been made to continue evaluating the project, detailed design typically begins. During detailed design, the FEL-1 design package is updated and additional deliverables are developed. Additional alternatives analysis may also be performed during this phase.
Detailed design is typically completed as either an FEL-2 design, which generally includes process engineering deliverables, or an FEL-3 design, which includes engineering deliverables and cost estimates from multiple disciplines, such as mechanical, civil, electrical, and instrumentation engineering. FEL-2 and FEL-3 are discussed below.
What Is Included in a FEL-2 Detailed Process Design Package?
Typical FEL-2 deliverables include:
- Updated HMB / process simulation / PFDs
- Piping and Instrumentation Diagrams (P&IDs)
- Updated Equipment List
- Updated or additional alternatives evaluations
- Instrument List
- Equipment Specification Sheets
- Instrument Specification Sheets
- Controls Narrative
- Material Selection Diagram
- Line Sizing
- Relief Device and Flare Sizing
- Process design-level capital cost estimate (±40%)
- Updated operating cost estimate
- Plot Plans
- Line List.
A complete FEL-2 design generally provides sufficient detail to improve the project cost estimate from approximately ±50% to ±40%. This estimate, together with an updated operating cost estimate, can be used by the client to determine whether the project should continue to the next phase of detailed design.
What Is Needed to Prepare a FEL-2 Design?
As with an FEL-1 design, the most important requirements for an FEL-2 design package are a detailed HMB and a clearly defined project design basis. Alternatives analysis should have been performed during FEL-1 to establish the major process flows and equipment. Adding major equipment, such as distillation columns or reactors, during FEL-2 can result in engineering rework, schedule delays, and cost overruns.
What Risks May Still Remain After Completing an FEL-2?
Once the FEL-2 deliverables are complete, most of the process engineering design has been developed. However, much of the design work associated with other engineering disciplines typically remains. Common unknowns at this stage include:
- Environmental permitting requirements
- Scope of other engineering disciplines, such as civil and electrical engineering.
- Lead times for equipment
- Capital cost estimate at ±40%.
What Is Included in an FEL-3 Detailed Engineering Design Package?
An FEL-3 design package is the detailed engineering package for a project and includes input from all necessary engineering disciplines. At this stage, most process engineering is complete, and only minor changes to the process flow diagram are typically expected.
Typical FEL-3 deliverables, in addition to the FEL-2 deliverables, include:
- Piping Design Package (3D Model, Isometrics, etc.)
- Civil and Structural Engineering Packages
- Electrical and Instrumentation Design Packages
- Material Take-offs
- Bid Package Preparation
- Capital cost estimate
- Project Schedule.
A complete detailed design results in a further refined capital cost estimate, typically within ±30%. This cost estimate can be used to support a final investment decision and move the project into the procurement and construction phases.
Summary
Chemical process design development can generally be divided into preliminary process design, such as FEL-0 and FEL-1, and detailed process design, such as FEL-2 and FEL-3. Understanding what is included in each phase—and equally important, what is not included—helps clients better understand project risks, make informed decisions, and avoid unnecessary cost and schedule impacts. If you are considering an engineering design for your process, please reach out to us. PROCESS has helped many clients across a wide range of industries design and revamp their processes.