How EPC Buyers Can Compare Tower Internals Engineering Proposals

Technical Guide | Tower Internals Engineering | KEMVORI Petrochemical Equipment Limited

Direct Engineering Answer

EPC buyers should compare tower internals engineering proposals against the same technical scope, not simply compare the final quoted prices.

Two suppliers may offer equipment for the same column, but their engineering deliverables, hydraulic calculations, mechanical design responsibilities and manufacturing scope can be significantly different.

A technically meaningful comparison should evaluate:

Process design basis and operating conditions.

Hydraulic calculation scope and results.

Equipment sizing and configuration.

Mechanical drawings and vessel interfaces.

Material specifications.

Fabrication and inspection requirements.

Engineering approval responsibilities.

Commercial exclusions and project risks.

A quotation that excludes hydraulic calculations, interface coordination or detailed manufacturing drawings may appear less expensive while transferring additional engineering work and project risks to the EPC contractor.

The objective is to identify the proposal that provides the most appropriate technical solution, clearly defined responsibilities and acceptable total project cost.

Why Comparing Tower Internals Proposals Is Difficult

Consider an EPC contractor requesting quotations for a packed absorption column.

Three suppliers submit proposals.

All three quotations mention tower internals design and manufacturing.

However, the first supplier includes preliminary equipment selection and standard product dimensions. The second includes hydraulic calculations and customized arrangement drawings. The third offers a lower equipment price but excludes detailed engineering and vessel interface coordination.

Comparing the three total prices alone does not establish which proposal provides the best technical value.

The differences may become apparent only after the purchase order is issued, when additional engineering charges, drawing revisions or interface modifications are requested.

This problem is particularly common in tower revamp projects, where existing vessel dimensions, process conditions and installation restrictions can significantly affect equipment design.

A structured technical bid evaluation should therefore take place before commercial selection.

1. Establish One Common Technical Basis

The first requirement is to ensure that every supplier evaluates the same project conditions.

Without a common technical basis, differences in equipment pricing may simply reflect different design assumptions.

Process Design Data

Provide the same process datasheets to all bidders.

The technical basis should identify:

Vapor flow rates.

Liquid flow rates.

Operating pressure.

Operating temperature.

Vapor and liquid densities.

Liquid viscosity.

Relevant fluid composition.

Minimum, normal and maximum operating cases.

Standard and actual gas volumetric flow rates must be clearly distinguished.

If process data are incomplete, all suppliers should receive the same provisional assumptions and clarification requirements.

Column and Vessel Dimensions

Provide the latest available vessel GA and relevant internal drawings.

Important information includes:

Column inside diameter.

Support ring elevations.

Nozzle locations.

Existing internal components.

Manway dimensions.

Available installation clearances.

For replacement projects, identify whether the dimensions come from original construction drawings or recent site measurements.

Equipment Performance Requirements

Define the required process and hydraulic performance criteria.

Depending on the application, this may include:

Maximum allowable pressure drop.

Required vapor and liquid capacity.

Flooding margin.

Liquid distribution requirements.

Operating turndown.

Separation or mass-transfer objectives.

A supplier cannot be fairly evaluated against a performance requirement that has not been consistently communicated.

2. Compare Hydraulic Calculation Deliverables

Hydraulic engineering is one of the most important areas to examine when comparing tower internals proposals.

A supplier may state that hydraulic design is included without identifying the actual calculations or operating cases covered.

EPC buyers should request a clear description of the engineering scope.

Vapor and Liquid Loading

Confirm whether the supplier evaluates the specified vapor and liquid loads.

The proposal should identify the operating cases included in the assessment.

A calculation based only on normal operating conditions may not address the required maximum capacity or minimum turndown.

Pressure-Drop Evaluation

Check whether the proposal includes pressure-drop calculations for the relevant equipment.

The calculation boundary should be clearly defined.

For example, a proposal may include packing pressure drop but exclude the pressure drop of support grids, collectors or other tower internals.

These differences matter when the project has a limited overall column pressure-drop allowance.

Flooding and Capacity Assessment

Determine whether the supplier evaluates relevant capacity limitations and flooding conditions.

Ask which operating cases and calculation methods are included.

A general statement such as "high-capacity design" is not a substitute for a defined engineering assessment.

Liquid Distribution Review

For distributors and redistributors, confirm whether the supplier evaluates the outlet arrangement, liquid loading and distribution requirements.

The engineering proposal should identify the equipment geometry being assessed.

Calculation Reports and Assumptions

A meaningful hydraulic deliverable should identify:

Process input data.

Operating cases.

Equipment geometry.

Calculation methods.

Key assumptions.

Calculation results.

Applicable limitations.

KEMVORI supports project-based hydraulic calculation and engineering review, including vapor-liquid loading analysis, pressure-drop evaluation, flooding assessment and liquid distribution review, depending on the agreed project scope and available process information.

The calculation scope should be defined before commercial comparison rather than assumed from a general statement of engineering capability.

3. Compare Engineering Drawings and Design Deliverables

Engineering drawings determine how the proposed equipment will fit, connect and be manufactured.

EPC buyers should distinguish between preliminary sketches and detailed engineering deliverables.

General Arrangement Drawings

Check whether the supplier provides equipment arrangement drawings showing the major dimensions, elevations and internal configuration.

Mechanical Interface Drawings

For projects involving existing or newly fabricated vessels, confirm whether the proposal includes relevant interface details.

These may include:

Support ring locations.

Support beam arrangements.

Attachment details.

Nozzle interfaces.

Installation clearances.

Component connections.

Fabrication Drawings

Determine whether detailed fabrication drawings are included.

A preliminary arrangement drawing is not equivalent to a complete manufacturing drawing package.

Fabrication documents may need to identify component dimensions, material specifications, welding details, tolerances and assembly requirements.

Installation Drawings

For segmented internals or restricted-access installations, check whether the supplier provides section identification, assembly arrangements and installation sequence information.

These deliverables can be particularly important during short plant shutdowns.

4. Compare Material Specifications and Traceability

Material differences can create substantial variations in equipment price.

However, a material specification should not be evaluated on price alone.

Check whether each proposal clearly identifies:

Material grade.

Product form.

Nominal thickness.

Applicable material standards.

Material certificates.

Traceability requirements.

Welding and fabrication requirements.

For stainless steel components, verify the exact grade rather than accepting a general description such as stainless steel.

For polymer internals, review the specified material grade and its suitability for the operating chemical environment and temperature.

For ceramic components, consider the applicable product specifications, dimensions and inspection requirements.

If suppliers propose different materials, the EPC team should establish whether the alternatives meet the same project requirements before comparing their prices.

5. Evaluate Engineering Responsibility and Approval Boundaries

One of the most overlooked differences between engineering proposals is the allocation of technical responsibility.

A supplier may provide manufacturing drawings without taking responsibility for the complete process design.

Another may include a defined hydraulic assessment but exclude pressure vessel structural design.

These differences should be visible in the technical proposal.

Confirm:

Who provides the process design basis.

Who performs hydraulic calculations.

Who prepares mechanical arrangement drawings.

Who verifies vessel interfaces.

Who approves the final equipment arrangement.

Who is responsible for manufacturing drawings.

Who provides inspection documentation.

Who authorizes fabrication release.

The EPC contractor should also identify which deliverables require owner or project engineering approval.

Supplier drawing preparation does not automatically transfer overall process or vessel design authority to the supplier.

6. Compare Quality Control and Inspection Requirements

Quality requirements should be compared against the same project specification.

Check whether the proposal includes:

Material inspection

Review material identification, certificates and applicable traceability requirements.

Dimensional inspection

Confirm whether critical dimensions and interfaces will be checked during manufacturing.

Welding inspection

Identify applicable welding procedures, inspection methods and acceptance criteria.

Fabrication inspection

Clarify which components and manufacturing stages are subject to inspection.

Final documentation

Confirm the required manufacturing records, inspection reports and final document package.

Do not assume that every supplier includes the same inspection scope in its quotation.

Additional inspection requirements may affect both manufacturing cost and delivery time.

7. Identify Commercial Exclusions and Hidden Project Costs

The lowest initial quotation may not represent the lowest total project cost.

EPC buyers should examine exclusions carefully.

Common exclusions include:

Hydraulic calculation reports.

Detailed engineering drawings.

Vessel interface coordination.

Material certificates.

Third-party inspection.

Additional drawing revisions.

Installation documentation.

Special packaging.

Site technical support.

Also check whether the quotation includes the complete equipment package or only selected components.

For example, a supplier may quote packing but exclude support grids, hold-down grids and liquid distributors.

If these components are necessary for the intended installation, their omission can create additional procurement and coordination work.

The commercial comparison should consider the cost of completing the entire required scope.

8. Common Mistakes in Technical Bid Evaluation

Selecting the Lowest Price Without Normalizing Scope

Different suppliers quote different engineering and manufacturing deliverables.

Engineering solution: Establish a common technical compliance list before comparing commercial totals.

Accepting Unverified Capacity Claims

A supplier claims improved column capacity without providing the relevant calculation basis.

Engineering solution: Request the operating cases, hydraulic methodology and assumptions supporting the claim.

Ignoring Existing Vessel Conditions

A proposed equipment arrangement is based on nominal column dimensions without checking actual support elevations and internal clearances.

Engineering solution: Require interface review against the latest available vessel drawings and site measurements where necessary.

Overlooking Engineering Exclusions

Hydraulic calculations and detailed drawings are excluded even though the proposal states that design is included.

Engineering solution: Request a deliverable-by-deliverable scope clarification.

Comparing Different Material Grades as Equivalent

Two quotations use different material specifications but are treated as technically identical.

Engineering solution: Obtain technical confirmation that each proposed material meets the project service conditions.

Ignoring Delivery and Manufacturing Risks

A supplier provides an attractive price but does not identify engineering approval milestones, material lead times or inspection requirements.

Engineering solution: Evaluate the manufacturing and documentation schedule alongside the quoted delivery date.

9. Engineering Trade-Off: Lowest Price vs. Lowest Project Risk

Selecting a supplier is not simply a matter of purchasing the most expensive engineering package.

An EPC contractor should purchase the engineering scope that is necessary for the specific project.

For a straightforward replacement using verified existing drawings and an unchanged process duty, a limited engineering scope may be sufficient.

For a new high-capacity installation or a major tower revamp, more extensive hydraulic calculations and mechanical interface coordination may be necessary.

The selection should consider:

Technical compliance.

Hydraulic calculation depth.

Mechanical design completeness.

Material suitability.

Manufacturing capability.

Inspection requirements.

Engineering approval responsibilities.

Total project cost.

Schedule and execution risk.

The best proposal is the one that meets the actual project requirements with clearly defined deliverables and acceptable technical and commercial risk.

10. Illustrative Project Scenario

Consider a hypothetical EPC project involving a packed absorption tower retrofit.

Three suppliers submit proposals for replacement packing and associated tower internals.

Supplier A offers the lowest initial price but excludes the liquid collector redesign.

Supplier B includes hydraulic calculations, a customized collector arrangement and vessel interface drawings.

Supplier C offers a higher price because its scope includes additional inspection and documentation requirements.

During technical evaluation, the EPC team identifies that the proposed packing replacement also requires a review of the existing collector arrangement.

Supplier A's initial quotation therefore does not cover the complete required scope.

The EPC team requests clarification from all three suppliers using the same technical basis.

The revised comparison includes hydraulic calculations, collector design, material specifications, inspection requirements and manufacturing deliverables.

The final selection is then based on technical compliance and total project scope rather than the original quotation totals alone.

This is how a structured technical bid evaluation prevents misleading price comparisons.

11. Acceptance Checklist Before Supplier Selection

Before recommending a tower internals supplier, confirm the following:

The final technical recommendation should document deviations, outstanding clarifications and any conditions attached to supplier selection.

12. What Should EPC Buyers Include in a Tower Internals Technical RFQ?

A well-prepared RFQ helps suppliers submit comparable proposals.

Include:

Project description and process service.

Approved process datasheets.

Vapor and liquid flow rates.

Operating pressure and temperature.

Fluid physical properties.

Column dimensions and vessel drawings.

Existing tower internals arrangement.

Required equipment configuration.

Material specifications.

Hydraulic calculation requirements.

Engineering drawing requirements.

Inspection and quality requirements.

Required delivery schedule.

Commercial quotation format.

The RFQ should also request a separate list of deviations, exclusions and assumptions.

This makes it easier to identify technical differences before the commercial evaluation is finalized.

Frequently Asked Questions

Should EPC buyers select tower internals suppliers based on price?

No. Price should be evaluated alongside hydraulic engineering scope, equipment configuration, material specifications, manufacturing requirements and project risks.

What hydraulic calculations should be included in a tower internals proposal?

Depending on the application, they may include vapor-liquid loading, pressure drop, flooding assessment, liquid distribution and equipment capacity evaluation.

Why are engineering drawings important when comparing suppliers?

Drawings establish the proposed equipment geometry, mechanical interfaces, installation arrangement and manufacturing requirements. Their level of detail should be clearly identified.

Should suppliers provide a list of technical exclusions?

Yes. Exclusions and assumptions should be disclosed so that EPC buyers can compare equivalent project scopes.

Can a supplier with a higher quotation provide better overall value?

Yes, if the additional cost represents necessary engineering, quality, inspection or manufacturing deliverables that reduce project risks and avoid later variations.

What is the most important document in a technical bid evaluation?

There is no single document that replaces a complete evaluation. The common RFQ technical basis, supplier compliance statement, calculation deliverables, drawings and commercial exclusions should be reviewed together.

Engineering Support from KEMVORI

KEMVORI Petrochemical Equipment Limited provides engineering review and customized tower internals solutions for distillation, absorption, refining, petrochemical and industrial gas-liquid separation applications.

Our engineering support can include:

Tower internals engineering review.

Process data and RFQ evaluation.

Hydraulic calculation support.

Vapor-liquid loading analysis.

Pressure-drop assessment.

Flooding evaluation.

Liquid distribution review.

Equipment sizing and arrangement.

Mechanical interface coordination.

Customized tower internals design and fabrication.

The exact engineering deliverables depend on project requirements, available process information and the agreed technical scope.

For an EPC project evaluation, provide your RFQ, process datasheets, column drawings, required equipment specifications and hydraulic performance criteria.

KEMVORI can review the available information and identify the engineering calculations, equipment configuration and manufacturing scope required for your project.

Submit your RFQ and technical specifications for engineering review.

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