Condensate Polishing & Feedwater Engineering for Sugar Mill Cogeneration Plants

1. Executive Summary & Process Overview

In modern integrated sugar complexes and bagasse-based cogeneration facilities, thermal efficiency and asset longevity rely on high-pressure steam generation (typically operating between 67 barg and 110 barg at superheat temperatures of 485°C to 540°C). Generating ultra-pure steam at these elevated pressures requires stringent boiler feedwater (BFW) quality to prevent catastrophic turbine blade deposition, superheater tube failure, and boiler drum foaming.

Evaporator condensate recovered from the sugar mill's multiple-effect evaporator (MEE) train represents up to 80% to 90% of total boiler feedwater makeup. While recycling condensate yields thermal heat recovery (saving millions of kJ/h) and minimizes fresh water intake, raw sugar mill condensate carries critical contaminants:

1. Sucrose Trace Carryover (C_{12}H_{22}O_{11}): Entrained juice drops from evaporator vapor spaces. Under high boiler drum temperatures (>300^\circC), sucrose thermally pyrolyzes into volatile organic acids (acetic, lactic, formic acids) and carbonaceous char. This causes catastrophic pH collapse (down to pH 4.5–5.2) and severe acidic corrosion in economizers and drum surfaces.
2. Volatile Organics & Ammonia: Thermal degradation of amino acids in cane juice releases volatile amines and ammonia into Vapor 1 and Vapor 2, raising raw condensate pH while increasing organic carbon loading.
3. Lubricating Oil & Hydrocarbon Contamination: Mill drive turbine gland leaks, pump seals, and heavy oil lubricated bearings introduce emulsified hydrocarbons into return condensate headers.
4. Dissolved Gases (O_2, CO_2): Ingress of atmospheric air during low-load operation or raw water makeup saturates condensate with dissolved oxygen, driving aggressive pitting corrosion in carbon steel pipework.

       +-------------------------------------------------------------------+
       |                 SUGAR FACTORY EVAPORATOR TRAIN                    |
       |  +-------------+   +-------------+   +-------------+   +--------+  |
       |  |  Effect I   |   |  Effect II  |   | Effect III  |   |Effect IV| |
       |  +------+------+   +------+------+   +------+------+   +---+----+  |
       +---------|-----------------|-----------------|--------------|------+
                 | Vapor 1         | Vapor 2         | Vapor 3      | Vapor 4
                 v                 v                 v              v
           [ High Quality ]  [ Med-High Quality]  [ High Organic ] [ Foul / Reject ]
           [ Condensate   ]  [  Condensate     ]  [ Sugar Trace  ] [ Condensate   ]
                 |                 |                 |              |
                 +--------+--------+                 v              v
                          |                     [ Divert / ]   [ Process Use / ]
                          v                     [ Process  ]   [ ETP Treatment ]
              +-----------------------+
              | OIL / SUGAR GUARD &   | <--- Online Refractometer & TOC Divert
              | TRACE REMOVAL SYSTEM  |
              +-----------+-----------+
                          |
                          v
              +-----------------------+
              | CONDENSATE POLISHING  | <--- Mixed Bed / Powdered Resin CPU
              |   UNIT (CPU SYSTEM)   |
              +-----------+-----------+
                          | Polished Condensate (< 0.2 µS/cm, TOC < 0.2 ppm)
                          v
              +-----------------------+
              | HIGH-PRESSURE SPRAY   | <--- LP Steam & Chemical Oxygen Scavenger
              |   CUM TRAY DEAERATOR  |
              +-----------+-----------+
                          | Feedwater (DO < 7 ppb, 105 - 130°C)
                          v
              +-----------------------+
              |  HIGH-PRESSURE COGEN  | (67 barg - 110 barg)
              |     BOILER SYSTEM     |
              +-----------------------+

To enable safe condensate recycling, a robust condensate treatment block must incorporate continuous online quality monitoring with fast divert valves, guard filters for oil and sugar, ion exchange condensate polishing units (CPU), and a high-performance mechanical thermal deaerator.

---

2. Detailed Mechanical & Process Design Parameters

Designing feedwater systems for sugar mill cogeneration plants requires adherence to international mechanical pressure vessel codes, shell-and-tube design standards, and water purity specifications.

2.1 Applicable International Codes & Standards

• ASME Section I: Power Boilers (Drum design, piping integrity, safety valves).
• ASME Section VIII, Division 1: Unfired Pressure Vessels (Deaerator storage tanks, CPU ion exchange columns, carbon filters).
• ASME PTC 19.11: Steam and Water Sampling, Conditioning, and Analysis in the Power Cycle.
• TEMA Class R: Tubular Exchanger Manufacturers Association standards for condensate heat recovery exchangers.
• API 650 / API 650 Appendix X: Welded Tanks for Oil/Condensate Storage (Duplex and Austenitic stainless steel fabrications).

2.2 Material & Metallurgical Selection Matrix

Because sugar condensate can instantly shift from neutral to highly acidic during an evaporator carryover upset, metallurgical selection must resist volatile organic acid corrosion and chloride-induced stress corrosion cracking (SCC).

---

3. Sizing Equations, Mass & Energy Balance, and Thermodynamic Logic

3.1 Evaporator Condensate Entrainment & Thermal Pyrolysis Logic

Sucrose (C_{12}H_{22}O_{11}) entrained in vapor decomposes under thermal stress inside the boiler drum according to two primary pathways:

1. Complete Aerobic Oxidation:

C_{12}H_{22}O_{11} + 12 O_2 \xrightarrow{Δ} 12 CO_2 + 11 H_2O

2. Anaerobic Thermal Pyrolysis (Acidogenesis):

C_{12}H_{22}O_{11} \xrightarrow{Δ, >250^\circC} 4 CH_3COOH  (Acetic Acid) + 4 HCOOH  (Formic Acid) + Carbonaceous Char

The sudden generation of hydrogen ions (H^+) depresses boiler water pH according to:

pH = -\log_{10} [H^+]

For every 1 ppm of sucrose entrained and pyrolyzed, up to 0.7 ppm of volatile organic acid is generated, driving boiler drum pH down from 9.5 to <5.5 within minutes.

3.2 Condensate Polishing Unit (CPU) Hydrosizing Equations

The design of a Deep-Bed Mixed Bed Condensate Polishing Unit requires balancing linear hydraulic velocity (u_v), resin bed contact time, and vessel pressure drop (Δ P).

              Q (m³/h) High-Purity Condensate Inlet
                              |
                              v
                   +---------------------+
                   |   Distribution Hub  |
                   +----------+----------+
                              |
            ==================v==================
            |  Strong Acid Cation (SAC) Resin   |   Bed Depth L = 1.0 - 1.5 m
            |  Strong Base Anion (SBA) Resin    |   Hydraulic Void Fraction ε = 0.38 - 0.40
            ==================+==================
                              |
                              v
                   +---------------------+
                   |  Johnson Screen Hub |
                   +----------+----------+
                              |
                              v
                  Polished Outlet (ΔP via Carman-Kozeny)

Linear Specific Velocity (u_v):

u_v = (Q) / (A_{bed)} = (4 Q) / (π  ·  D_{vessel)²}

Where:

• Q = Condensate volumetric flow rate (m³/h)
• A_{bed} = Cross-sectional area of the resin vessel (m²)
• D_{vessel} = Internal diameter of CPU vessel (m)
• Operating range for CPU service: u_v = 30 to 60 m/h (higher than standard demineralizer beds due to low ion load).

Pressure Drop (Δ P) Across Monosphere Resin Bed (Carman-Kozeny Equation):

Δ P = (150  ·  μ  ·  u_v  ·  L  ·  (1 - \epsilon)²) / (d_p²  ·  \epsilon³)

Where:

• Δ P = Pressure drop across the resin bed (Pa)
• μ = Dynamic viscosity of condensate at operating temperature Pa·s (Note: at $80^\circ\text{C}$, μ ≈ 0.355 × 10^{-3} Pa·s)
• u_v = Superficial linear velocity (m/s)
• L = Resin bed depth (m), typically $1.0\text{ m to } 1.5\text{ m}$
• \epsilon = Bed void fraction (typically $0.38 \text{ to } 0.40$)
• d_p = Mean harmonic diameter of resin beads (m), typically $0.60 \times 10^{-3}\text{ m}$ ($600,\mu\text{m}$)

Resin Operating Exchange Capacity Calculation:

The service run duration (T_{run}, hours) between regenerations is calculated by:

T_{run} = (V_{resin}  ·  C_{operating}) / (Q  ·  Σ (C_{in, i))}

Where:

• V_{resin} = Total ion exchange resin volume (m³)
• C_{operating} = Operating capacity of resin (eq/m³ or kgr/ft³)
• C_{in, i} = Total equivalent ionic concentration of ion i in condensate (eq/m³ or meq/L)

3.3 Deaerator Thermodynamic & Dissolved Gas Mass Balance

Deaeration operates on Henry's Law and Dalton's Law of Partial Pressures.

Henry's Law:

C_g = K_H(T)  ·  P_g

Where:

• C_g = Equilibrium concentration of dissolved gas (O_2 or CO_2) in liquid phase (mg/L)
• K_H(T) = Temperature-dependent Henry's Law constant (mg/L·bar^{-1})
• P_g = Partial pressure of the gas above the liquid film (bar)

As steam heats the incoming condensate droplets to saturation temperature (T_{sat} at deaerator operating pressure), the solubility constant K_H(T) approaches zero. Concurrently, scrubbing steam sweeps away liberated gases, driving P_g \to 0, forcing C_g \to 0.

                            Steam Phase (P_steam)
     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
          |              |              |              |
          v              v              v              v
     +---------+    +---------+    +---------+    +---------+
     | Droplet |    | Droplet |    | Droplet |    | Droplet |  Condensate Droplets
     | (T_sat) |    | (T_sat) |    | (T_sat) |    | (T_sat) |  (K_H -> 0)
     +----+----+    +----+----+    +----+----+    +----+----+
          |              |              |              |
          +--------------+--------------+--------------+
                         |
                         v (O2, CO2 liberated to steam vapor phase)
             Stripped Gas Venting (P_g -> 0)

Heat and Mass Balance Equations across Spray-cum-Tray Deaerator:

  Condensate Inlet (m_cond, h_cond)          Pegging Steam (m_steam, h_steam)
                 |                                      |
                 v                                      v
          +----------------------------------------------------+
          |              DEAERATOR SPRAY CHAMBER               |
          |       +------------------------------------+       |
          |       |     PERFORATED TRAY CASCADE TIER   |       |
          |       +------------------------------------+       |
          +-------------------------+--------------------------+
                                    |
                                    +---> Vent Losses (m_vent, h_vent)
                                    |
                                    v
                       Deaerated Feedwater Outlet
                        (m_fw = m_cond + m_steam - m_vent)
                        (h_fw @ saturation temp T_sat)

Overall Mass Balance:

m_{fw} = m_{cond} + m_{steam} - m_{vent}

Overall Energy (Enthalpy) Balance:

m_{cond}  ·  h_{cond} + m_{steam}  ·  h_{steam} = m_{fw}  ·  h_{fw} + m_{vent}  ·  h_{vent}

Substituting m_{fw}:

m_{steam} = (m_{cond}  ·  (h_{fw} - h_{cond}) + m_{vent}  ·  (h_{vent} - h_{fw})) / (h_{steam) - h_{fw}}

Where:

• m_{cond}, m_{steam}, m_{fw}, m_{vent} = Mass flow rates of condensate, pegging steam, feedwater, and vent steam (kg/h)
• h_{cond} = Specific enthalpy of incoming condensate (kJ/kg)
• h_{steam} = Specific enthalpy of incoming heating steam (kJ/kg)
• h_{fw} = Specific enthalpy of saturated liquid in storage tank (kJ/kg)
• h_{vent} = Specific enthalpy of vented vapor mixture (kJ/kg)

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4. Boiler Feedwater Quality Standards: High-Pressure Cogeneration

To prevent boiler tube failures caused by caustic gouging, hydrogen damage, or overheating due to scale formation, feedwater must comply with ASME Consensus Guidelines for Water Quality in Modern Industrial Boilers (ASME CRTD-Vol 34).

4.1 ASME Water Quality Requirements by Pressure Class

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5. Contaminant Removal & Polishing Technology Architecture

                               RAW CONDENSATE INLET
                                        |
                                        v
                    +---------------------------------------+
                    |  Continuous Online Monitoring Hub     |
                    |  - Refractometric Sugar Detector      |
                    |  - Cation & Specific Conductivity     |
                    |  - High Temperature TOC Analyzer      |
                    +-------------------+-------------------+
                                        |
                     Pass Quality Check | Sugar / Oil Contamination Spike
                    +-------------------+-------------------+
                    |                                       |
                    v                                       v
      +---------------------------+           +---------------------------+
      | Triple-Deck Coalescer &   |           | Fast Actuating 3-Way      |
      | Oil Guard Filter          |           | Automatic Divert Valve    |
      +-------------+-------------+           +-------------+-------------+
                    |                                       |
                    v                                       v
      +---------------------------+           +---------------------------+
      | Deep-Bed Mixed Bed CPU /  |           | Process Water Storage /   |
      | Powdered Resin Unit       |           | Effluent Treatment Plant  |
      +-------------+-------------+           +---------------------------+
                    |
                    v
      +---------------------------+
      | Polished Condensate Header|
      | to Deaerator Storage Tank |
      +---------------------------+

5.1 Online Sugar Detection & Fast Divert Protection Assembly

Because sugar carryover can ruin millions of dollars in ion exchange resins within hours, a fast-divert system is the primary defense line:

1. Inline Differential Refractometer: Detects bulk sugar carryover (> 5 ppm) with a response time of < 2 seconds.
2. Cation Conductivity Analyzer: Measures organic acid breakdown products (HCOO^-, CH_3COO^-) following a miniature heated sample resin column. High cation conductivity (> 0.5 μS/cm) trips the system.
3. High-Temperature Combustion TOC Analyzer: Measures total organic carbon continuously down to $10\text{ ppb}$.
4. Fast-Acting Pneumatic 3-Way Valve: Switches condensate flow from the CPU feed header to the Effluent Treatment Plant (ETP) or raw juice imbibition tank within 3 to 5 seconds of an alarm threshold breach.

5.2 Oil Separation Technology (Coalescing & Guard Filtration)

Hydrocarbon ingress from turbine seals and mechanical gearboxes is removed using a dual-stage setup:

• Stage 1: Oleophilic Coalescing Filter: Matrix of polypropylene microfiber media forces micro-emulsified oil droplets ($1 - 5,\mu\text{m}$) to coalesce into macroscopic droplets (> 50 μm), which float to a top skim chamber.
• Stage 2: Granular Activated Carbon (GAC) Guard Bed: Macroporous coconut-shell activated carbon absorbs dissolved hydrocarbons, protecting downstream ion exchange resins from oil-coating fouling.

5.3 Condensate Polishing Units: Mixed Bed vs. Powdered Resin Systems

Deep-Bed Mixed Bed Polisher:

Contains an intimate mixture of Strong Acid Cation (SAC) resin in H^+ form and Strong Base Anion (SBA) resin in OH^- form at a volumetric ratio of 1:1 to 1:2 (SAC:SBA).

• Mechanism:

Cation Exchange:  R-H^+ + Na^+ \rightleftharpoons R-Na^+ + H^+

Anion Exchange:  R-OH^- + Cl^- \rightleftharpoons R-Cl^- + OH^-

Neutralization:  H^+ + OH^- \rightleftharpoons H_2O

• Resin Fouling Mitigation: Sugar molecules can become physically trapped within standard microporous resin pores, degrading kinetics and promoting bacterial slime growth. To prevent this, macroporous resins with structured pore diameters (> 40 nm) are specified.

Powdered Resin Filter/Polisher (Precoat System):

Uses finely ground SAC and SBA resins ($40 - 70,\mu\text{m}$) precoated onto inert SS316L wedge-wire element septums. The precoat acts as a 5-micron mechanical filter and an ion exchange bed simultaneously.

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6. Comparative Selection Matrix: CPU Technologies

The selection of a condensate polishing system for a sugar mill cogeneration plant depends on raw condensate quality, thermal profile, capital availability, and operational philosophy.

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7. Deaeration Engineering & Thermal Degasification

Thermal deaeration removes dissolved oxygen (O_2) and carbon dioxide (CO_2) to non-corrosive levels (< 7 ppb O_2) while raising feedwater enthalpy prior to the economizer.

7.1 Spray-cum-Tray Deaerator Architecture

                  UNPOLISHED / POLISHED CONDENSATE INLET
                                    |
                                    v
                    +-------------------------------+
                    |  Spring-Loaded Spray Nozzles  |  (Atomizes into 50-100 µm droplets)
                    +---------------+---------------+
                                    |
                                    v
    +---------------------------------------------------------------+
    |                  TRAY CHAMBER (SS316L / DUPLEX 2205)          |
    |  +---------------------------------------------------------+  |
    |  |  Tier 1: Perforated Distribution Trays                  |  |
    |  +---------------------------------------------------------+  |
    |  |  Tier 2: Interlocking Cascade Trays                     |  |
    |  +---------------------------------------------------------+  |
    |  |  Tier 3: Counter-Current Steam Scrubbing Zone           |  |
    |  +---------------------------------------------------------+  |
    +-------------------------------+-------------------------------+
                                    |
                                    v
    +---------------------------------------------------------------+
    |             HORIZONTAL BFW STORAGE TANK (ASME SEC VIII)       |
    |                                                               |
    |  ~~~~~~~~~~~~~~~~ Saturated Water Level ~~~~~~~~~~~~~~~~~~~  |
    |                                                               |
    +-------------------------------+-------------------------------+
                                    |
                                    v
                       BFW PUMP SUCTION (NPSHA > NPSHR)

1. Spray Valve Atomization Zone:

Incoming condensate enters the upper deaerator dome through spring-loaded variable-orifice spray valves constructed from SS316L or Duplex 2205. The valves atomize the water into small droplets ($50 - 100,\mu\text{m}$ diameter), maximizing the gas-liquid interfacial area per unit mass:

a = (6) / (ρ_w  ·  d_m)

Where:

• a = Specific surface area (m²/kg)
• d_m = Mean droplet diameter (m)

This rapid surface expansion heats condensate to within $1 - 2^\circ\text{C}$ of saturation temperature in milliseconds, liberating up to 90% to 95% of dissolved gases.

2. Tray Cascade Scrubbing Zone:

Water flows downward by gravity over a series of staggered, perforated cascade trays manufactured from Duplex 2205 (UNS S31803). Low-pressure pegging steam ($1.5 - 3.5\text{ barg}$, extracted from turbine exhaust or Vapor 1) flows counter-currently upward through the tray perforations. The scrubbing action strips remaining trace oxygen molecules down to < 7 ppb.

7.2 Mechanical Shell Sizing (ASME Section VIII Div 1)

The horizontal storage vessel provides thermal surge capacity (typically sized for 15 to 20 minutes of continuous maximum boiler feed pump demand).

Shell Wall Thickness Calculation (t):

t = (P_{design}  ·  R) / (S  ·  E - 0.6  ·  P_{design)} + C_a

Where:

• t = Minimum required shell thickness (mm)
• P_{design} = Internal design pressure (MPa or N/mm²), typically $1.10 \times \text{Maximum Operating Pressure}$
• R = Inside radius of storage tank shell (mm)
• S = Maximum allowable stress value for shell material (MPa) (e.g., SA-516 Grade 70 carbon steel at $150^\circ\text{C} \approx 138\text{ MPa}$)
• E = Joint efficiency factor (1.0 for 100% Radiographic Testing per UW-11A)
• C_a = Corrosion allowance (mm), typically $3.0\text{ mm}$ for boiler feedwater service.

7.3 Chemical Oxygen Scavenging

While mechanical deaeration reduces dissolved oxygen to < 7 ppb, chemical oxygen scavengers are dosed into the deaerator storage tank outlet line to scavenge residual dissolved oxygen down to absolute zero (< 1 ppb).

         O2 Removal Efficiency vs Operating Temperature
  100% +------------------------------------------------------***  (Target: < 1-3 ppb)
       |                                                 *****
   80% |                                            *****
       |                                       *****
   60% |                                  *****
       |                             *****
   40% |                        *****
       |                   *****
   20% |              *****
    0% +--------------+-------------------+-------------------+
      20°C          60°C                100°C               125°C
                      Temperature (°C)

Chemical Scavenger Selection Analysis:

1. Sodium Sulfite (Na_2SO_3):

2 Na_2SO_3 + O_2 \to 2 Na_2SO_4

• Limitation: Strictly prohibited in boilers operating above $60\text{ barg}$. At elevated drum temperatures (>280^\circC), sodium sulfite thermally decomposes into corrosive gases:

Na_2SO_3 + H_2O \xrightarrow{Δ} 2 NaOH + SO_2 \uparrow

4 Na_2SO_3 \xrightarrow{Δ} 3 Na_2SO_4 + Na_2S \quad (promotes  H_2S  acid attack)

• Sodium sulfite also increases Boiler Total Dissolved Solids (TDS), necessitating higher blowdown rates.

2. Hydrazine (N_2H_4):

N_2H_4 + O_2 \to 2 H_2O + N_2 \uparrow

• Passivates magnetite layers on steel tubes:

6 Fe_2O_3 + N_2H_4 \to 4 Fe_3O_4 + 2 H_2O + N_2 \uparrow

• Limitation: Known human carcinogen; handling requires strict environmental controls.

3. Carbohydrazide ((N_2H_3)_2CO) - Preferred Standard:

(N_2H_3)_2CO + 2 O_2 \to 2 N_2 \uparrow + 3 H_2O + CO_2 \uparrow

• Non-volatile, safe-to-handle solid organic compound. Hydrolyzes at temperatures above $135^\circ\text{C}$ into hydrazine and carbon dioxide, providing volatile passivating protection throughout superheaters and steam turbine circuits without adding TDS to the boiler drum.

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8. Real-World Industrial Case Study & Performance Validation

8.1 Facility Profile & Baseline Engineering Challenge

• Facility: Integrated 10,000 TCD Sugar Mill & 45 MW Cogeneration Power Plant.
• Boiler Specification: 110 TPH Water-tube Boiler operating at $87\text{ barg}$ and $515^\circ\text{C}$ superheat steam.
• Baseline Configuration: Mixed evaporator condensate (Vapor 1 through Vapor 4) fed directly to an old atmospheric spray deaerator without condensate polishing.

Operating Problems Observed:

1. Periodic sugar entrainment spikes (> 20 ppm) caused boiler water pH to drop from 9.5 down to 5.1, requiring emergency boiler trips.
2. Silica carryover (SiO_2 > 0.08 ppm) in superheated steam caused hard glass scale deposits on HP turbine first-stage nozzles, degrading turbine efficiency by 6.4% per campaign.
3. Severe pitting corrosion in the economizer header due to high dissolved oxygen ($45\text{ ppb}$) from poor deaerator tray design.

8.2 Systems Engineering Retrofit Executed by SEMCO

1. Condensate Segregation & Guard Installation: Segregated condensate streams. Vapor 3 and 4 condensate diverted to process imbibition. Vapor 1 and 2 ($120\text{ TPH}$) routed through an automated inline sampling skid containing continuous refractive index detectors and cation conductivity meters linked to a 3-way fast-divert valve.
2. Installation of Deep-Bed CPU: Installed a 2x100% duty Macroporous Deep-Bed Mixed Bed Condensate Polishing Unit featuring Duplex 2205 Johnson-screen strainers and SS316L vessel lining.
3. Deaerator Upgrade: Replaced atmospheric deaerator with an ASME Section VIII Div 1 certified Spray-cum-Tray Pressurized Deaerator ($2.1\text{ barg}, 135^\circ\text{C}$) built with SS316L spray valves and Duplex 2205 tray assemblies. Dosing shifted from sodium sulfite to carbohydrazide.

8.3 Field Performance Validation & Operating Results Data

              BOILER WATER SILICA & pH TREND (PRE VS POST RETROFIT)
  pH Scale                                                     Silica Scale (ppm)
  10.0 +=======================================================+ 0.00
       | pH (Post-Retrofit Stable: 9.4)                         |
   9.0 +-------------------------------------------------------+ 0.02 (ASME HP Limit)
       |                                                       |
   8.0 +                                      Silica (Post:0.01)| 0.04
       |                                                       |
   7.0 +                                                       | 0.06
       |                                                       |
   6.0 +                                                       | 0.08
       | pH Upset (Pre-Retrofit: 5.1)   Silica (Pre: 0.09)     |
   5.0 +-------------------------------------------------------+ 0.10
       Day 1   Day 5   Day 10   Day 15   Day 20   Day 25   Day 30

The table below documents field analytical measurements pre- and post-retrofit over a 120-day continuous crushing season:

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9. Conclusion & Engineering Best Practices

Recycling sugar mill evaporator condensate into high-pressure cogeneration boilers requires stringent process boundaries, robust equipment design, and automated safety controls.

9.1 Core Engineering Checklist

  [✓] STEP 1: SEGREGATE CONDENSATE STREAMS
      - Route Vapor 1 & 2 to CPU / Boiler Feed
      - Route Vapor 3, 4 & 5 to Process / Imbibition / ETP

  [✓] STEP 2: DUAL-GUARD FAST DIVERT ASSEMBLY
      - Install Refractometer + Cation Conductivity + TOC Skid
      - Configure 3-Way Pneumatic Fast-Divert Valve (< 3-sec actuation)

  [✓] STEP 3: SPECIFY METALLURGY FOR CORROSION & ACID SHOCKS
      - Raw condensate lines: SS316L (UNS S31603)
      - CPU internal strainers & Deaerator trays: Duplex 2205 (UNS S31803)
      - Chemical injection quills: Hastelloy C-276 (UNS N10276)

  [✓] STEP 4: SELECTION & HYDROSIZING OF CPU
      - Select Macroporous Monosphere Resins to prevent organic fouling
      - Design linear flow velocity within 30 - 60 m/h

  [✓] STEP 5: PRESSURIZED THERMAL DEAERATION
      - Upgrade to ASME Sec VIII Div 1 Spray-cum-Tray Deaerator
      - Ensure mechanical gas removal to < 7 ppb DO
      - Dose Carbohydrazide in place of Sodium Sulfite for boilers > 60 barg

By integrating continuous TOC monitoring, macroporous mixed-bed condensate polishing, and pressurized tray-type deaeration, sugar mill cogeneration facilities can maintain ASME-compliant feedwater purity ($<0.2,\mu\text{S/cm}cation conductivity,<0.02\text{ ppm}silica,<2\text{ ppb } O_2$), protecting boiler and turbine assets while maximizing thermal energy recovery.