6 Duplex 2205 Distillation Columns and Heat Exchangers for Sulzer Chemtech: 138.5-Ton Isomer Column & Falling Film Reboilers for India’s BALPLA Bioplastics Project

Lmart manufactured six large-scale Duplex 2205 pressure vessels for Sulzer Chemtech’s BALPLA polylactic acid (PLA) bioplastics project in India — including a 138.5-ton, 49-meter Isomer Separation Column and a 69-ton Crude Lactide Column, along with two falling film reboilers and two hammer condensers. All units are certified to ASME U Stamp with IBR (Indian Boiler Regulations) compliance where required, designed for the corrosive lactic acid environment of industrial-scale PLA monomer purification.

Customer	Sulzer Chemtech (headquartered in Winterthur, Switzerland)
Industry	Bioplastics — polylactic acid (PLA) monomer purification
Project	BALPLA — large-scale PLA production facility, India
Equipment	Distillation Columns × 2, Falling Film Reboilers × 2, Hammer Condensers × 2 (6 units total)
Design Code	ASME Section VIII Div. 1 (U Stamp) + IBR (Indian Boiler Regulations)
Key Materials	Duplex 2205 (UNS S31803), SA516 Gr.70
Max Single-Piece Weight	138,500 kg (Isomer Separation Column)
Max Single-Piece Length	49 m (Isomer Separation Column)
Total Shipping Weight	≈ 247,355 kg (6 units combined)

Customer Background and Industry Context

Sulzer Chemtech, a division of Sulzer Ltd. headquartered in Winterthur, Switzerland, is a global leader in separation, mixing, and reaction technology. The company designs and licenses complete process plants for petrochemical, fine chemical, and bioplastics applications — specifying and procuring the critical rotating and static equipment from qualified fabricators worldwide.

The BALPLA project is one of the largest polylactic acid (PLA) production facilities under construction in India. PLA is a biodegradable thermoplastic derived from renewable feedstocks (corn starch, sugarcane) that serves as a sustainable alternative to petroleum-based plastics in packaging, textiles, and 3D printing. The production process converts lactic acid into lactide monomer through oligomerization, depolymerization, and purification — the purification stage being where the columns and heat exchangers in this project operate.

Lactide purification is the bottleneck that determines PLA product quality. Crude lactide contains meso-lactide (an optical isomer), residual lactic acid, water, and oligomeric impurities that must be separated to achieve the ≥99.5% L-lactide purity required for high-molecular-weight PLA. This separation is performed in vacuum distillation columns operating at elevated temperatures — conditions that are simultaneously corrosive (lactic acid attacks austenitic stainless steels through pitting and crevice corrosion) and thermally sensitive (lactide degrades and racemizes above certain temperature thresholds). The material selection, column internals design, and heat exchanger configuration must all be optimized to balance separation efficiency against thermal degradation.

Challenges and Engineering Pain Points

Extraordinary Scale: 138.5 Tons in a Single Vessel

The Isomer Separation Column weighs 138,500 kg and measures 49 meters in length — one of the largest single vessels Lmart has ever manufactured. At DN3700 diameter with 30 mm wall thickness in Duplex 2205, this column pushes the limits of plate rolling, circumferential seam welding, and heat treatment capacity. The 30 mm wall thickness reflects the combined demands of large diameter, internal vacuum/pressure cycling, and the mechanical properties of Duplex 2205 at elevated temperature. Each circumferential weld on a DN3700 vessel requires precise fit-up across a >11.6-meter circumference, with post-weld heat treatment (PWHT) considerations specific to duplex stainless steel — where time-temperature control is critical to avoid sigma phase precipitation that degrades both toughness and corrosion resistance.

The Crude Lactide Column, while smaller at 69,000 kg and 32 meters, presents its own complexity: a variable-diameter design with DN3300 and DN3000 sections at different elevations and wall thicknesses of 14, 16, and 24 mm. The diameter transition requires a conical reducer section that must maintain full-penetration weld integrity and code-compliant stress analysis at the geometric discontinuity.

Duplex 2205: Corrosion Resistance with Fabrication Constraints

Duplex 2205 (UNS S31803) was selected across all six units for its resistance to lactic acid corrosion — specifically its high pitting resistance equivalent number (PREN ≥ 34) and resistance to stress corrosion cracking at the temperatures encountered in lactide distillation. However, Duplex 2205 imposes strict fabrication constraints that do not apply to conventional austenitic grades:

• Ferrite/austenite phase balance. The weld metal and heat-affected zone (HAZ) must maintain 30–70% ferrite content to preserve both corrosion resistance and toughness. Excessive ferrite (>70%) reduces toughness and chloride SCC resistance; insufficient ferrite (<30%) reduces strength and pitting resistance. This requires controlled heat input during welding, appropriate filler metal selection (typically ER2209 with slightly elevated nickel), and strict interpass temperature limits (≤150 °C).
• Sigma phase avoidance. Duplex 2205 is susceptible to sigma phase formation when held in the 600–1000 °C range. Any PWHT or stress relief must be performed as a solution anneal above 1040 °C followed by rapid water quench — a procedure that is logistically challenging on vessels exceeding 40 meters in length. Where possible, Lmart engineered the welding sequences to minimize residual stress and avoid the need for full solution annealing of completed assemblies.
• Impact testing at low temperature. Duplex 2205 must demonstrate adequate toughness at the minimum design metal temperature (MDMT). Charpy impact tests are performed on both weld metal and HAZ specimens to verify that the phase balance achieved during production welding delivers the specified toughness values.

IBR Certification: Indian Regulatory Requirements

Four of the six units require IBR (Indian Boiler Regulations) certification in addition to ASME U Stamp. IBR is India’s mandatory regulatory framework for pressure vessels operating above specified pressure/temperature thresholds. IBR certification adds a parallel layer of requirements to the ASME fabrication process:

• All pressure-retaining materials must be procured from IBR-approved mills with IBR-stamped mill test certificates
• Welding procedures must be separately qualified and approved by the Chief Inspector of Boilers
• Third-party inspection by an IBR-authorized inspector at defined hold points — material identification, fit-up, welding, NDE, hydrostatic test, and final inspection
• A separate IBR documentation package including Form III-A calculations, material certificates, and inspection reports, submitted to the inspectorate for vessel registration

Managing dual ASME + IBR documentation and inspection schedules on six large vessels simultaneously requires rigorous production planning to avoid hold-point conflicts and inspection delays.

Falling Film Reboiler Design for Heat-Sensitive Lactide

The two falling film reboilers in this project are not conventional kettle or thermosiphon reboilers. A falling film reboiler is a vertical shell-and-tube heat exchanger where the process liquid is distributed as a thin film flowing downward by gravity over the outside (or inside) of the tubes. The thin film provides extremely short residence time and uniform heat transfer — critical for lactide, which racemizes (converts from the desired L-form to the undesired D/meso-form) when exposed to high temperatures for extended periods. The design challenge is achieving sufficient heat transfer area for the required reboil duty while maintaining film uniformity across all tubes — dry patches lead to local overheating and product degradation, while flooding defeats the purpose of the falling film configuration.

Why Sulzer Chemtech Selected Lmart

Proven heavy-vessel fabrication capacity. Manufacturing a 138.5-ton, 49-meter column in Duplex 2205 requires plate rolling equipment, welding positioners, and workshop crane capacity that most fabricators do not possess. Lmart’s workshop infrastructure handles vessels of this scale routinely for LNG, petrochemical, and marine applications — the same cranes and positioners used for ASME-coded LNG vaporizers and large-diameter ship condensers support the column fabrication workflow.

Duplex stainless steel welding expertise. Lmart has extensive production experience with Duplex 2205 and Super Duplex 2507 across marine and chemical projects, with qualified welding procedures, trained welders, and in-house ferrite measurement capability (feritscope and metallographic examination) to verify phase balance on production welds.

ASME U Stamp + IBR dual certification experience. Managing parallel ASME and IBR documentation streams, inspection hold points, and material traceability requirements is a capability that Lmart has developed through previous export projects to the Indian market. The quality team understands IBR inspector expectations and documentation formats, reducing the risk of inspection delays.

Repeat customer relationship. Sulzer Chemtech has previously sourced falling film equipment from Lmart for projects in Singapore and Brazil. This established relationship provides Sulzer with confidence in Lmart’s quality system, delivery performance, and technical communication — particularly important for a project of this scale and complexity where mid-fabrication engineering changes are inevitable.

Engineering and Manufacturing Solution

The six vessels form an integrated lactide purification train: two distillation columns perform the primary separation, each paired with a dedicated falling film reboiler for gentle re-evaporation and a hammer condenser for vapor recovery.

Crude Lactide Column — variable-diameter tower design. The Crude Lactide Column features a dual-diameter configuration: DN3300 in the upper section and DN3000 in the lower section, with wall thicknesses varying from 14 mm to 24 mm across different elevation zones. This variable-diameter design reflects the different vapor/liquid traffic at different stages of the distillation — the upper rectifying section handles higher vapor volumes (requiring larger diameter for acceptable vapor velocity), while the lower stripping section operates with higher liquid loading at reduced diameter. The conical transition between sections is a critical fabrication element: the cone angle, weld geometry, and local stress reinforcement must satisfy ASME VIII Div. 1 requirements for conical shell-to-cylinder junctions (UG-36 and Appendix 1-5), with additional finite element analysis to verify stress distribution at the discontinuity under all operating load combinations.

Isomer Separation Column — the 138.5-ton centerpiece. At DN3700 with 30 mm Duplex 2205 walls, this column is the largest and heaviest single vessel in the project. The 49-meter overall length means the column is fabricated in multiple shop sections and either field-assembled or transported as sub-assemblies requiring specialized heavy transport. The 30 mm wall thickness is driven by the combination of large diameter, internal vacuum service (lactide distillation operates under vacuum to reduce boiling temperature and minimize thermal degradation), and the elevated-temperature mechanical properties of Duplex 2205. Each shell course requires plate rolling on equipment capable of handling 30 mm duplex plate to the tight tolerances specified by ASME for out-of-roundness and peaking at longitudinal and circumferential seams.

Falling film reboilers — gentle re-evaporation for lactide service. Both reboilers use a bimetallic construction: SA516 Gr.70 carbon steel shells with Duplex 2205 tube bundles. The carbon steel shell handles the heating medium (typically steam or hot oil) on the shell side, where corrosion conditions are benign. The Duplex 2205 tubes carry the lactide process fluid, where lactic acid corrosion resistance is essential. This bimetallic approach optimizes material cost — using expensive duplex alloy only where the process chemistry demands it. The Crude Lactide reboiler (DN2400 × 18 mm, 36,275 kg) and Isomer Separation reboiler (DN2500 × 20 mm, 34,850 kg) are both substantial vessels in their own right, with tube-to-tubesheet welds performed in Duplex 2205 requiring individual ferrite verification.

Hammer condensers — lactide vapor recovery. The two hammer condensers reverse the bimetallic arrangement: Duplex 2205 shells with SA516 Gr.70 tubes. Here, the lactide vapor contacts the shell side (requiring duplex corrosion resistance), while the cooling medium flows through the carbon steel tubes. The hammer condenser design uses a specific baffle configuration optimized for condensing service — promoting effective vapor distribution and condensate drainage while minimizing pressure drop across the tube bundle. Both units are DN2200 × 12 mm at approximately 6.2 m length, with the Isomer Separation unit slightly heavier (19,540 kg vs. 18,190 kg) reflecting differences in internal baffle and nozzle configurations.

Duplex 2205 vs. Austenitic Stainless Steels for Lactic Acid Service

Property	304L / 316L (Austenitic)	Duplex 2205 (UNS S31803)
PREN	~18 (304L) / ~25 (316L)	≥ 34
Yield Strength (min)	170–205 MPa	450 MPa
Chloride SCC Resistance	Poor (304L) / Moderate (316L)	Excellent — resistant to ≥120 °C
Lactic Acid Corrosion	Susceptible to pitting above 60 °C	Resistant at process temperatures
Fabrication Complexity	Standard — no phase balance concerns	High — strict heat input, interpass temp, ferrite control
Relative Material Cost	1× (304L) / 1.3× (316L)	~1.8×
Justification in This Project	Insufficient pitting resistance for lactic acid at temperature	Required for long-term reliability in lactide distillation service

The universal selection of Duplex 2205 for all process-wetted components reflects Sulzer’s engineering standard for PLA plants: the higher material and fabrication cost is justified by the 20+ year design life expectation and the catastrophic consequences of a corrosion-induced leak in a column containing hot lactide under vacuum.

Complete Equipment Specifications

#	Equipment	Qty	Material	DN (mm)	Wall (mm)	Weight (kg)	Length (m)	Code
1	Crude Lactide Column	1	Duplex 2205	3300 / 3000	14 / 16 / 24	69,000	32	ASME U + IBR
2	Isomer Separation Column	1	Duplex 2205	3700	30	138,500	49	ASME U + IBR
3	Crude Lactide Falling Film Reboiler	1	Shell: SA516 Gr.70 / Tube: Duplex 2205	2400	18	36,275	5	ASME U + IBR
4	Crude Lactide Hammer Condenser	1	Shell: Duplex 2205 / Tube: SA516 Gr.70	2200	12	18,190	6.2	ASME U
5	Isomer Separation Falling Film Reboiler	1	Shell: SA516 Gr.70 / Tube: Duplex 2205	2500	20	34,850	4	ASME U + IBR
6	Isomer Separation Hammer Condenser	1	Shell: Duplex 2205 / Tube: SA516 Gr.70	2200	12	19,540	6.2	ASME U

Project Execution, Quality Control, and Delivery

The fabrication sequence was planned around the two columns as critical-path items, with the heat exchangers scheduled in parallel on separate workshop bays. Duplex 2205 material was procured from a single mill lot where possible to minimize heat-to-heat variation in phase balance and mechanical properties.

Key QC milestones across all six vessels:

• Incoming material verification: mill certificates cross-referenced against ASME SA-240 (plate) and SA-789/SA-790 (tube/pipe) requirements, plus IBR material endorsement stamps for the four IBR-certified units
• Duplex 2205 plate and weld metal ferrite measurement: feritscope readings at minimum 5 locations per plate/weld, confirming 30–70% ferrite content per ASTM E562 and NORSOK M-601
• Welding procedure qualification with Charpy impact testing at MDMT, bend tests, and metallographic examination of weld metal and HAZ for phase balance verification
• Shell course rolling with dimensional verification: out-of-roundness ≤1% of diameter, peaking at longitudinal seams ≤3 mm per ASME UG-80
• 100% radiographic testing (RT) of all longitudinal and circumferential butt welds per ASME UW-51
• Hydrostatic pressure test per ASME UG-99 with test pressure held for minimum 30 minutes at 1.3× MAWP, witnessed by Authorized Inspector and IBR inspector (where applicable)
• Solution annealing of critical duplex welds where residual stress analysis indicated risk of sigma phase formation during service temperature excursions
• Corrosion testing (ASTM A923 Method C) on production test coupons to confirm absence of detrimental intermetallic phases
• IBR Form III-A documentation package preparation and submission to the Chief Inspector of Boilers for vessel registration

Transport planning for the 138.5-ton, 49-meter Isomer Separation Column required coordination with specialized heavy-lift logistics providers. Depending on final transport routing, the column may be shipped as multiple shop-welded sections with field girth welds completed at the BALPLA plant site — a common approach for ultra-long columns where road transport clearances and port crane capacity constrain single-piece dimensions.

Results and Business Impact

The six vessels constitute the core separation and heat transfer equipment for BALPLA’s lactide purification section — the process step that ultimately determines PLA polymer quality. Duplex 2205 construction throughout the process-wetted surfaces provides long-term corrosion reliability in the lactic acid environment, supporting the plant’s 20+ year design life without scheduled pressure-boundary replacements.

The falling film reboiler configuration enables gentle re-evaporation of heat-sensitive lactide with minimal thermal degradation and racemization — directly impacting the optical purity of the final L-lactide product and, consequently, the mechanical properties and commercial value of the PLA polymer produced downstream.

For Lmart, this project represents a landmark in fabrication scale: the 138.5-ton Isomer Separation Column ranks among the heaviest single vessels ever manufactured at the Zhangjiagang facility. Combined with the dual ASME U + IBR certification requirement and the Duplex 2205 material specification, the project demonstrates Lmart’s position as a qualified supplier for globally engineered process plants where equipment specifications are set by European technology licensors and installed in regulated markets worldwide.

The BALPLA project also reinforces Lmart’s growing track record with Sulzer Chemtech, following previous falling film equipment deliveries for Sulzer projects in Singapore and Brazil. Repeat business from a customer of Sulzer’s caliber — a company that maintains a global approved vendor list with rigorous qualification criteria — is a meaningful endorsement of manufacturing quality and project execution capability.

Customer Voice

Sulzer Chemtech selected Lmart for the BALPLA column and heat exchanger package based on demonstrated heavy-vessel fabrication capacity, duplex stainless steel welding expertise, and successful delivery history on previous Sulzer falling film equipment projects.

“The ferrite control on the duplex welds was consistently within specification across all production welds. The dual ASME and IBR documentation was managed without inspection delays.”

— Sulzer Chemtech project engineering team (paraphrased from project review)

Note: Lmart respects client confidentiality. Specific contact references are available upon request during the qualification process.