Activated Carbon SRU Revamping, Retrofitting & Rebuilding

DEC as an experienced solvent-recovery modernization contractor: DEC can assess existing Solvent Recovery Units (SRUs), including systems manufactured by other vendors, and develop technically defined revamping, retrofitting, refurbishment or rebuilding strategies. Particular attention can be given to activated-carbon bed condition, regeneration performance, condensation, utilities, controls and the recovery of otherwise wasted thermal energy through DEC.THR™ Thermal Heat Recovery and DEC.ULP™ Ultra-Loop™.

Activated Carbon SRU Modernization: Beyond Maintenance

An existing activated-carbon Solvent Recovery Unit can often be improved without replacing the complete installation. The appropriate scope depends on the condition of the adsorbers and activated carbon, the regeneration method, solvent chemistry, airflow, emission requirements, utility consumption, automation condition and the future production envelope.

For mature installations, the modernization opportunity is often not limited to restoring the original performance. A retrofit can introduce more efficient regeneration, improved heat integration, updated controls, improved condensation or a dedicated energy-recovery architecture.

1. Start With an SRU Engineering Condition Assessment

The first phase should establish a documented technical baseline rather than assuming that the original design remains representative of present operating conditions.

• Adsorber vessel and internal condition.
• Activated-carbon type, age, loading history, attrition and pressure drop.
• Adsorption airflow, solvent concentration, humidity and temperature.
• Regeneration temperature, flow, pressure and cycle duration.
• Heating equipment, thermal-fluid circuit or electrical heating system.
• Condensers, chillers, separators and recovered-solvent handling.
• Fans, valves, dampers and actuators.
• PLC, HMI, instrumentation, analyzers and safety functions.
• Historical solvent recovery, emissions, energy and downtime data.
• Mass-balance information for recovered solvent, water, impurities and downstream purification streams.
• Current and future production requirements.

The assessment should separate measured performance, documented equipment information and assumptions requiring site verification.

2. Refurbish, Retrofit, Rebuild or Replace?

2.1 Refurbishment

Refurbishment restores existing SRU equipment and functionality without fundamentally changing the process architecture. Typical activities include activated-carbon replacement, gasket and seal renewal, valve servicing, equipment cleaning, heat-exchanger cleaning, instrument replacement and control-component renewal.

2.2 Retrofit

Retrofit adds new technology or functionality while retaining usable parts of the existing SRU. Typical retrofit measures include energy recovery, improved regeneration, upgraded controls, new or modified condensers, instrumentation and process-integration improvements.

2.3 Rebuild

Rebuild involves deeper reconstruction of major subsystems where refurbishment alone is insufficient but the overall installation can still provide a viable foundation. The scope may include adsorber internals, activated-carbon beds, valves, thermal equipment, condensers, ducting, piping and automation, while retaining selected existing equipment where technically justified.

2.4 Replace

Replacement should be considered when the existing vessels, process architecture or installed capacity cannot reasonably support the future operating envelope, or when the required modernization would approach the scope, risk and cost of a new SRU. Replacement is therefore the appropriate path when the existing equipment cannot provide a technically viable foundation for the required future duty.

Customer Question: Can a Steam-Regenerated SRU Be Converted to Dry Nitrogen Regeneration?

Why the conversion is not a simple connection change

A steam-regenerated SRU is engineered around the physical and thermodynamic characteristics of steam. The regeneration temperature, heating duty, condensation behaviour, piping and drainage arrangements, valves, instrumentation and operating sequence are all coordinated with the steam-based process. A dry nitrogen regeneration system uses a different regeneration medium and normally operates with a different temperature profile, gas circulation arrangement and solvent-condensation strategy.

• Temperature: the existing adsorber vessels, carbon support systems, seals and internals must be checked against the temperature required by the proposed nitrogen regeneration process.
• Process architecture: the regeneration circuit must be redesigned around a closed or controlled nitrogen circulation loop rather than a steam supply and steam-condensate system.
• Connections: existing steam, condensate, vent, drain, nitrogen and regeneration-gas connections are not automatically interchangeable. Nozzle sizes, locations, piping, valves and equipment interfaces must be verified or modified.
• Heating system: nitrogen regeneration requires a suitable method of heating the circulating regeneration gas and controlling its temperature. The existing steam heat-transfer arrangement may not provide the required process configuration or control.
• Condensation and solvent recovery: removing steam from the regeneration gas changes the gas composition and condensation duty. The condenser, separator, cooling system and recovered-solvent handling arrangement therefore require reassessment.
• Pressure and vessel design: the proposed regeneration pressure and gas circulation conditions must be checked against the pressure rating and mechanical design of the existing adsorbers and associated equipment.
• Controls and safety: the PLC sequence, temperature protection, valve interlocking, nitrogen management, solvent concentration control and safety functions must be re-engineered for the new operating principle.

What can be retained?

Conversion does not necessarily mean that the complete SRU must be discarded. Depending on the original design and condition, selected items such as adsorber vessels, structural supports, condensers, cooling equipment, fans, instrumentation, piping sections or auxiliary systems may be technically reusable. Each item must, however, be verified against the new process conditions, connections, materials, pressure and temperature ratings and required performance.

When a steam-to-nitrogen conversion should be considered

A steam-to-nitrogen conversion should be treated as a process re-engineering and modernization project, not as a conventional maintenance retrofit. The feasibility study should establish the existing SRU heat and mass balance, vessel design conditions, carbon operating envelope, regeneration cycle, utility interfaces and available space, then define the new nitrogen regeneration circuit and its integration with solvent condensation and energy recovery.

Where the objective is to eliminate steam consumption and improve thermal efficiency, the study can also evaluate DEC.SRU_RSG™ nitrogen regeneration together with DEC.THR™ Thermal Heat Recovery and DEC.ULP™ Ultra-Loop™. The technically appropriate solution depends on the existing SRU and the required future operating envelope.

A full-electric conversion should therefore be distinguished from simply installing an electric heater in place of an existing steam heat exchanger. The electrical heating system, thermal circuit, heat-transfer surfaces, controls, protection functions and utility interfaces must be engineered as an integrated system. Where the existing thermal-fluid circuit can be retained, DEC.IEB™ In-Line Electric Booster can also be evaluated as a retrofit solution. Depending on the required duty, the booster can supplement an existing boiler or, when sized appropriately, provide the complete thermal duty of the circuit.

Where the objective is deeper electrification, an existing SRU heating arrangement can be evaluated for conversion to full-electric heating. DEC's e-SRU™ full-electric configuration provides an electrified SRU architecture in which regeneration heating is supplied electrically rather than by a fossil-fuel-fired utility. For brownfield plants, the feasibility of converting the existing heating circuit to electric service depends on the existing thermal-fluid loop, required heat duty, electrical power availability, transformer capacity, cable routing, process temperatures, control architecture and the condition and rating of existing heat exchangers and pressure equipment.

Full-electric heating conversion

For activated-carbon regeneration, DEC.HHX™ can be considered where the required high-temperature thermal-fluid supply exceeds the temperature available from the existing plant utility. The hybrid arrangement uses available plant heat for preheating and electrical energy for the final temperature lift. This can be particularly relevant to brownfield SRU projects where existing boilers, thermal-fluid systems, CHP/CCHP recovered heat or electrical infrastructure need to be integrated rather than discarded.

DEC.HHX™ Hybrid Heat Exchanger is specifically developed for retrofit integration where the existing site utility can provide part of the required thermal duty, while an integrated electric booster supplies the remaining temperature lift. The architecture can combine existing thermal-fluid or saturated-steam utilities with electric heating, allowing the existing SRU infrastructure to be modernized without automatically replacing the complete heating system.

DEC.HHX™ Hybrid Heat Exchanger integration

3. Activated Carbon Adsorption System

Gas-phase adsorption is the core separation mechanism in an activated-carbon SRU. Solvent-laden air passes through activated carbon, where VOC molecules are retained on the porous adsorbent. When the working loading is reached, the bed is removed from adsorption service and regenerated. DEC describes this cyclic adsorption and regeneration sequence as the core operating principle of DEC.SRU™ systems.

3.1 What to Review

• Bed dimensions and superficial velocity.
• Carbon grade and particle-size distribution.
• Carbon loading and remaining adsorption capacity.
• Pressure drop and evidence of fouling.
• Humidity exposure and water co-adsorption.
• Carbon attrition, dust generation and support-screen condition.
• Temperature distribution during regeneration.

3.2 Adsorption Performance vs. Process Changes

A plant expansion, changed solvent mixture, higher humidity or altered process capture can make an originally adequate SRU operate outside its optimum envelope. Modernization should therefore reassess the adsorption cycle against the present and future Solvent-Laden Air (SLA) conditions.

4. Activated Carbon Condition and Replacement

Activated carbon is a consumable process medium and a major determinant of SRU performance. Carbon replacement should be based on condition and process requirements rather than simply elapsed operating time.

• Loss of adsorption capacity.
• Excessive pressure drop.
• Mechanical attrition or fragmentation.
• Thermal degradation or localized overheating.
• Contamination by oils, particulates or incompatible substances.
• Changes in solvent chemistry that require a different carbon grade.

Where carbon replacement is required, the project should include removal, temporary containment, new-carbon loading, dust control, bed leveling and recommissioning. The activated-carbon specification should be matched to the actual solvent mixture, humidity, concentration and regeneration method.

5. Regeneration Circuit and Process Performance

Regeneration is often the largest energy-consuming portion of an SRU. In a nitrogen-regenerated DEC.SRU_RSG™ system, hot nitrogen is used to desorb solvents from the activated-carbon bed before the desorbed stream is condensed and recovered. DEC identifies nitrogen regeneration as a TSA process and describes heat recovery as an integral energy-efficiency opportunity.

5.1 Regeneration Parameters

• Regeneration temperature and temperature ramp.
• Nitrogen circulation flow.
• Regeneration pressure.
• Cycle duration and endpoint criteria.
• Heating duty and thermal losses.
• Cooling duty and return temperature.
• Solvent concentration in regeneration gas.
• Water content and dehydration requirements.

5.2 Regeneration Optimization

Optimization can target shorter regeneration time, lower external heating duty, reduced cooling duty, improved solvent recovery and better utilization of the installed carbon inventory. These objectives must be balanced against carbon temperature limits, solvent properties, flammability and recovered-solvent quality.

6. DEC.THR™ Thermal Heat Recovery

DEC.THR™ Thermal Heat Recovery is part of DEC.ULP™ Ultra-Loop™ energy-recovery architecture for SRUs. DEC describes THR as a thermal-energy recovery process that recovers energy associated with the SRU regeneration cycle and returns it to the process.

6.1 Why Thermal Recovery Matters

During regeneration, energy is supplied to heat the regeneration medium and activated-carbon bed. During subsequent cooling and condensation, a significant portion of that thermal energy must be rejected. A properly engineered recovery circuit can transfer part of this energy back into the regeneration process, reducing external heating demand and associated cooling duty.

6.2 THR as a Retrofit Opportunity

For an existing SRU, THR can be evaluated without assuming that the entire adsorption system must be replaced. The feasibility depends on available space, existing regeneration architecture, heat-exchanger arrangement, temperature levels, utilities, controls and the physical configuration of the SRU.

7. DEC.ULP™ Ultra-Loop™ Energy Recovery

DEC.ULP™ Ultra-Loop™ is a modular energy-recovery architecture developed specifically for solvent-recovery applications. DEC describes it as a closed thermal loop with heat-exchange and thermal-storage functions that captures regeneration heat and makes it available for reuse.

7.1 Core Energy-Recovery Concept

The objective is to reduce the amount of external energy required to regenerate the activated carbon while simultaneously reducing the energy required to reject heat during cooling and condensation.

7.2 THR Architectures Within the ULP Family

DEC identifies DEC.THR₅™ and DEC.THR₇™ as complementary process architectures within the DEC.ULP™ family. The appropriate architecture is selected according to the thermal characteristics and configuration of the installation.

7.3 Retrofit Compatibility

A central feature of DEC.ULP™ is its modular retrofit approach. Existing SRUs can be assessed for integration of energy-recovery modules, heat exchangers, thermal storage, modified regeneration circuits and associated controls. The exact retrofit scope is determined from the existing process architecture and heat balance.

8. THR / ULP Retrofit Architecture

An SRU energy-recovery retrofit should be engineered as a complete thermal balance. The review should identify where heat is generated, where it is rejected, where it can be recovered and at what temperature level it can be reused.

1. Establish the existing regeneration and condensation heat balance.
2. Measure or reconstruct heating and cooling utilities.
3. Identify recoverable heat streams and temperature levels.
4. Check available footprint and tie-in locations.
5. Evaluate heat-exchanger pressure drop and fan implications.
6. Define thermal storage requirements where applicable.
7. Integrate temperature, flow and safety instrumentation.
8. Update PLC/HMI sequencing and alarms.
9. Commission the recovery loop progressively and validate the revised heat balance.

DEC describes ULP as particularly applicable to existing SRU installations requiring an energy-efficiency upgrade without necessarily replacing the complete adsorption system.

8.1 Hybrid Sorption and RBC Integration

SRU modernization can also be considered as part of a broader sorption architecture. Where technically appropriate, DEC.HSU™ Hybrid Sorption Unit can integrate rotary-bed concentration with activated-carbon solvent recovery.

The process route may be configured according to stream concentration and recoverability. Dilute streams can be considered for rotary-bed concentration before solvent recovery, while suitable higher-concentration streams can be routed directly to the SRU. Other arrangements, including downstream concentration or polishing, may be evaluated where justified by the process conditions.

This is a high-level modernization concept only. The detailed HSU architecture, operating envelope and selection criteria will be addressed separately.

9. Condensation, Cooling and Solvent Quality

Regeneration energy recovery cannot be separated from solvent condensation. The regeneration gas leaving the activated-carbon bed contains desorbed solvent and thermal energy. Condensation recovers the solvent while rejecting or recovering heat.

• Condenser duty and approach temperature.
• Cooling-water or chilled-fluid consumption.
• Recovered-solvent temperature and phase separation.
• Water content and solvent purity.
• Potential freezing or crystallization risks.
• Chiller COP and electrical consumption.
• Heat recovery opportunities before final cooling.

DEC.SRU™ configurations can use different regeneration approaches including nitrogen, steam, vacuum and direct condensation depending on solvent chemistry, concentration, humidity, emission requirements and recovery objectives.

9.1 BCS™ Chiller Upgrades: Refrigerants, Temperature and Cycle Time

The cooling side of an existing SRU can also be modernized. A DEC.BCS™ Brine Chiller System upgrade can be considered where the existing refrigeration package is obsolete, inefficient, no longer aligned with current refrigerant requirements, or unable to provide the temperature and cooling duty required by the modernized SRU.

• Frigorigenic fluid upgrade: the refrigeration circuit can be evaluated for a modern refrigerant configuration appropriate to the application, environmental requirements, safety classification and applicable regulations. DEC.BCS™ supports different refrigerant configurations, including low-GWP options, subject to project-specific selection.
• Lower process temperatures: where the solvent chemistry, condensation duty and refrigeration system permit, reducing the condensation temperature can increase the driving force for solvent condensation and may contribute to shorter process cycles. The effect is installation-specific and must be established from the solvent properties, condenser design, cooling duty, refrigeration COP and overall SRU cycle sequence.
• Cycle-time optimization: cooling performance should be assessed together with regeneration and condensation timing. A colder condenser is not automatically a faster SRU. The complete thermal balance, heat-transfer area, solvent loading, water content, chiller capacity and control sequence must be evaluated.
• Energy optimization: the objective is not simply to obtain the lowest possible temperature. The optimum BCS operating point should balance condensation performance, cycle time, electrical consumption, refrigerant efficiency and solvent recovery requirements.

9.2 Downstream Solvent Purification and Process Integration

An SRU modernization can extend beyond adsorption, regeneration and condensation to the downstream handling and purification of the recovered solvent. Where the recovered liquid requires water removal, impurity control or further purification before reuse, the complete recovery chain should be assessed rather than optimizing the SRU in isolation.

Downstream process optimization and debottlenecking

Process optimization can include reviewing the number and duty of downstream distillation columns, column operating conditions and internal heat-transfer or mass-transfer equipment. Where a distillation train contains a bottleneck, modification of column internals, heat-transfer surfaces or other process equipment may increase useful throughput without automatically adding a complete new column. In suitable cases, the process configuration can also be reconsidered to reduce the number of separation steps required for the target solvent specification.

For downstream solvent purification, DEC.DST™ distillation systems can be considered where thermal separation is required, while DEC.ADM™ Advanced Dehydration Modules can address water removal according to solvent chemistry, concentration and the required product specification.

Pre-dehydration and final molecular-sieve dehydration

Where the process requires staged dehydration, the modernization study can evaluate DEC.ADM_PHD™ or DEC.ADM_FDP™ as pre-dehydration stages, followed by a second dehydration stage using DEC.MZA™ molecular sieves. A liquid-phase molecular-sieve configuration such as DEC.ADM_UDS™ can be considered where the recovered solvent is already in liquid phase and residual water must be reduced to the required specification.

The selection and sequencing of these stages should be based on the solvent composition, water loading, impurity profile, recovered-solvent specification, temperature, pressure, phase condition and required throughput. The objective is to remove the appropriate water load at each stage while avoiding unnecessary thermal duty or oversized downstream equipment.

Mass-balance-driven equipment sizing

Before modifying condensers, heat exchangers, distillation equipment or dehydration systems, the modernization study should establish a reliable mass balance covering solvent species, water, impurities, recovered product, losses and recycle streams. A reconciled balance provides the basis for correctly sizing heat exchangers and condensers and for identifying how upstream SRU operating changes will alter downstream purification loads.

The same mass balance should be connected to the energy balance. Changes in regeneration temperature, condensation temperature, solvent concentration, water content or recovery rate can shift both the duty and temperature level of downstream distillation and dehydration equipment. Adsorption, regeneration, condensation, pre-dehydration, molecular-sieve dehydration and final purification should therefore be evaluated as one integrated solvent-recovery chain. Where a combined adsorption and separation architecture is appropriate, DEC.HSU™ Hybrid Sorption Unit can also be evaluated as part of the process-integration study.

10. Fans, Pressure Drop and Gas-Flow Optimization

An SRU retrofit must preserve the required adsorption airflow while accounting for pressure drop across activated carbon, filters, valves, heat exchangers and condensers.

• Measure actual SLA flow against the design range.
• Review carbon-bed pressure drop.
• Check filters and inlet conditioning.
• Assess fan operating point and motor loading.
• Review valve and damper pressure losses.
• Quantify any new pressure drop introduced by heat-recovery equipment.
• Consider VFD optimization and flow balancing.

DEC.SRU™ systems cover a wide range of industrial SLA volumes, with the DEC.SRU_RSG™ page identifying typical applications from approximately 5,000 to 1,000,000 Nm³/h. Actual retrofit feasibility remains installation-specific.

11. Controls, Instrumentation and Automation

Controls modernization can be an important part of an SRU retrofit because regeneration, valve sequencing, adsorption switching, heating, cooling, condensation and energy recovery are tightly coupled.

• PLC and HMI obsolescence.
• Cycle sequencing and permissives.
• Temperature and pressure measurement.
• VOC analyzers and adsorption-endpoint control.
• Nitrogen flow and regeneration control.
• Heat-recovery temperature and flow control.
• Chiller and cooling-system integration.
• Safety interlocks, alarms and trip functions.
• Data logging and performance monitoring.

DEC can coordinate automation modernization with SRU retrofit and refurbishment activities, including controls, instrumentation, safety functions and process optimization.

Where downstream purification is part of the modernization, control upgrades can also include vacuum control, temperature control, pressure measurement, flow measurement, valve positioning and coordinated sequencing for distillation, condensation and dehydration systems. The objective is to maintain stable vapor-liquid equilibrium and consistent separation performance as feed composition, solvent loading and production conditions change.

12. Process Safety and Solvent Service

SRU modernization must preserve the safety basis of the original installation and reassess it where process conditions or equipment are changed.

• Solvent flammability and autoignition characteristics.
• Oxygen concentration in inert-gas systems.
• Maximum carbon-bed temperature.
• Pressure and vacuum protection where applicable.
• Static electricity and grounding.
• Solvent compatibility of seals, gaskets and materials.
• Overtemperature detection and emergency shutdown.
• Nitrogen supply reliability and low-flow protection.
• Safe handling of solvent-contaminated carbon during maintenance.

Changing regeneration technology can be a major engineering change rather than a simple component retrofit. DEC's SRU engineering guide notes that adsorber vessels are designed and rated around the pressure and temperature conditions of their original regeneration method, so a conversion between steam, nitrogen and vacuum regeneration requires specific vessel and process assessment.

13. Capacity, Cycle Time and Production Changes

A modernization can target increased usable capacity by reducing regeneration time, improving heat transfer, restoring carbon performance or optimizing cycle control. Faster regeneration can make more adsorption capacity available over a given operating period.

DEC.ULP™ material identifies faster activated-carbon regeneration as one potential consequence of improved heat recovery and decoupled thermal management. Any capacity increase should nevertheless be demonstrated against the actual SLA flow, solvent loading, carbon inventory, regeneration limits, condensation capacity and emission target.

14. Energy, OPEX and Decarbonisation

Energy recovery and energy saving are central objectives of SRU modernization. A modernized solvent recovery system can reduce energy demand by reusing waste heat, applying advanced process configurations and optimizing activated-carbon regeneration cycles. The objective is not only to restore equipment, but to reduce the energy required per unit of recovered solvent while maintaining recovery performance, solvent quality and safe operation.

• Waste-heat reuse: DEC.THR™ Thermal Heat Recovery and DEC.ULP™ Ultra-Loop™ can recover thermal energy from the regeneration cycle and return usable heat to the process, reducing external heating requirements.
• Advanced regeneration: optimization of DEC.SRU_RSG™ TSA regeneration and the associated DEC.ULP™ energy-recovery architecture can reduce utility demand by improving heat recovery, regeneration-cycle timing and thermal integration. Depending on the configuration, this can reduce consumption of natural gas or other heating utilities, electricity and cooling energy.
• Lower OPEX: lower external thermal duty, reduced refrigeration demand, optimized fan power and shorter or better-controlled regeneration cycles can contribute to lower operating expenditure. Actual savings must be established from site-specific utility consumption, operating hours, solvent loading and energy prices.
• Process integration: advanced regeneration, condensation, DEC.MZA™ molecular-sieve dehydration, downstream purification and heat recovery should be evaluated as one energy and mass balance rather than as isolated equipment packages.
• Solvent reuse: recovering solvent rather than destroying it can reduce the need for virgin-solvent purchases and avoid the direct combustion emissions associated with thermal oxidation where solvent recovery is technically appropriate.
• Electrification: heating and auxiliary systems can be evaluated for electrification, including e-SRU™ configurations and hybrid DEC.HHX™ integration.
• Carbon-footprint accounting: quantify Scope 1 and Scope 2 effects using site-specific fuel and electricity data, while separately accounting for the avoided upstream footprint of virgin-solvent production where recovered solvent displaces new solvent purchases.

DEC publishes configuration-dependent ULP™ performance cases showing up to 53% reduction in SRU thermal heat balance and up to 55% reduction in cooling energy. These figures are not universal guarantees: the achievable saving depends on the existing SRU architecture, regeneration method, solvent loading, operating conditions, heat-recovery configuration and project-specific heat and mass balances.

Advanced regeneration and ULP energy recovery: the regeneration cycle is a major energy driver in an activated-carbon SRU. By recovering heat that would otherwise be rejected, optimizing regeneration-cycle timing and improving the thermal integration of heating, regeneration and condensation, DEC.ULP™ can reduce the external utility demand of the cycle. Depending on the selected configuration, the resulting savings may include natural gas or other thermal-fuel consumption, electrical energy and cooling energy. The economic effect should be evaluated as total OPEX, including fuel, electricity, refrigeration, cooling utilities, maintenance and solvent value.

Electrification can extend these decarbonisation benefits. Converting regeneration heating from steam or fossil-fuel-derived thermal utilities to a full-electric configuration can eliminate on-site combustion for the heating duty. Where electricity is supplied from a low-carbon source, the reduction in Scope 1 emissions can be substantial, while the actual Scope 2 impact depends on the site's electricity mix. The electrical conversion should therefore be evaluated together with heat recovery, cooling demand, electrical infrastructure and the site's decarbonisation strategy.

For brownfield installations, the modernization pathway may be staged. DEC.HHX™ can support hybrid thermal/electric integration where existing utility heat remains available, while a full-electric e-SRU™ configuration can be evaluated where the objective is a deeper transition away from steam or combustion-based heating. In both cases, DEC.THR™ and DEC.ULP™ energy recovery can reduce the external energy requirement before the remaining duty is electrified.

Reduced carbon footprint: solvent recovery can avoid direct combustion emissions that would otherwise result from solvent oxidation, while solvent reuse can reduce the need for fresh solvent purchases and the associated upstream production footprint. The direct combustion benefit is principally relevant to Scope 1 emissions; electricity consumption and its associated emissions are reflected in Scope 2. The avoided upstream manufacture and transport of virgin solvent should be accounted for separately as value-chain emissions rather than being presented as Scope 1 or Scope 2. Accordingly, the carbon benefit of SRU modernization should be quantified using the site's actual fuel consumption, electricity mix, recovered-solvent displacement and operating hours.

The broader DEC approach is to integrate solvent recovery and energy recovery so that VOC control, solvent reuse, energy efficiency, OPEX reduction and decarbonisation are addressed as one system rather than separate projects. DEC.SRU™ recovers solvent instead of combusting it, which can avoid combustion-related CO₂ and NOx associated with thermal oxidation and can reduce the need for fresh solvent production when the recovered solvent is returned to productive use.

15. Preliminary Feasibility for Third-Party SRUs

For an SRU manufactured by another vendor, DEC should obtain sufficient basic information before defining a revamp strategy. The preliminary feasibility review should not assume that hidden internal condition, vessel ratings or original design margins are known.

15.1 Minimum Information to Be Disclosed to DEC

• Recent photographs and, where possible, operating videos.
• Equipment technical data plate, manufacturer, model and serial number.
• General arrangement and layout drawings.
• P&IDs and process-flow diagrams.
• Adsorber vessel drawings and available design data.
• Activated-carbon specification, quantity, age and replacement history.
• Regeneration method and cycle parameters.
• Heating and cooling utility data.
• Condenser and chiller information.
• Fan curves, motor data and VFD information.
• PLC, HMI, instrumentation and electrical documentation.
• Historical solvent recovery and emission data.
• Maintenance records, known defects and recurring alarms.
• Current and expected SLA flow, solvent concentration, solvent mixture and humidity.
• Current environmental permit requirements and operating limits.
• Specific site rules, safety policies, permit-to-work requirements and contractor procedures.

The preliminary study should classify each item as documented, customer-provided or requiring site verification. This prevents a desktop feasibility review from being mistaken for a complete equipment inspection.

16. Shutdown Planning and Project Execution

SRU modernization is frequently constrained by production shutdowns. The scope should therefore be designed around the available outage window from the beginning.

16.1 Pre-Shutdown Work

• Engineering surveys and measurements.
• Fabrication of piping, skids and supports.
• Panel fabrication and PLC software development.
• Procurement of carbon, valves, heat exchangers and instruments.
• Factory testing of new assemblies where practical.

16.2 Shutdown Work

• Isolation and safe preparation.
• Carbon removal or containment where required.
• Mechanical dismantling of the retrofit area.
• Installation of new energy-recovery and process equipment.
• Carbon replacement or bed work.
• Electrical, instrumentation and control modifications.
• Tie-ins, pressure/leak checks and functional testing.

16.3 Commissioning

Commissioning should progress from dry checks to control-loop verification, valve sequencing, regeneration tests, heat-recovery commissioning, solvent introduction and performance verification. The revised heat balance and solvent recovery performance should be documented.

17. DEC SRU Modernization Framework

DEC can structure an existing-SRU modernization project through a staged engineering process:

1. Document review: collect equipment, process, utility, maintenance and site information.
2. Condition assessment: inspect adsorbers, carbon, regeneration, condensation, fans, valves and controls.
3. Performance baseline: quantify recovery, emissions, energy, pressure drop and cycle time.
4. Thermal assessment: establish the existing heating, cooling and condensation heat balance.
5. Mass-balance assessment: reconcile solvent, water, impurity, recovery and downstream purification flows and use the results to verify exchanger and condenser duties.
6. Energy-recovery study: evaluate DEC.THR™ and DEC.ULP™ retrofit options.
7. Process-integration study: evaluate downstream distillation debottlenecking, column-internal modifications and downstream dehydration and distillation integration where it can reduce energy demand or remove capacity constraints.
8. Option engineering: define refurbishment, retrofit, rebuild and replacement alternatives.
9. Lifecycle evaluation: compare CAPEX, OPEX, downtime, energy and future capacity.
10. Execution planning: freeze long-lead items and develop the shutdown strategy.
11. Implementation and validation: execute, commission and verify the agreed performance.

DEC provides dedicated DEC.RFT™ Retrofit and DEC.RFB™ Refurbish services for existing VOC abatement systems, including solvent recovery equipment. The scope can include adsorbers, activated-carbon beds, regeneration circuits, fans, valves, heat exchangers, instrumentation, automation, safety functions and process optimization.

Frequently Asked Questions

DEC Related Technologies and Services

Relevant DEC technologies and services for activated-carbon SRU modernization include:

• DEC.SRU™ Solvent Recovery Units
• DEC.SRU_RSG™ Nitrogen Regeneration
• DEC.SRU_RSV™ Steam Regeneration
• DEC.SRU_RTV™ Vacuum Regeneration
• DEC.THR™ Thermal Heat Recovery
• DEC.ULP™ Ultra-Loop™
• DEC.ERS™ Energy Recovery Solutions
• DEC.RFT™ Retrofit | DEC.RFB™ Refurbish
• DEC.TSS™ Technical Support Services
• DEC.HDS™ Help Desk Services
• DEC.HHX™ Hybrid Heat Exchanger
• DEC.IEB™ In-Line Electric Booster
• DEC.HSU™ Hybrid Sorption Unit
• DEC.RBC™ Rotary Bed Concentrator
• DEC.BCS™ Brine Chiller Systems
• DEC e-SRU™ Full-Electric Configuration

Engineering Disclaimer

This guide is general engineering information and does not replace a site-specific process study, equipment inspection, pressure-equipment assessment, safety review, environmental permitting assessment or detailed heat and mass balance. Actual retrofit, refurbishment and rebuilding scope must be determined from the specific SRU design, solvent chemistry, operating history, site conditions and applicable regulations. Published performance figures are configuration-dependent and require project-specific verification.