Compendium

Walkthrough — Design a Turbomachinery Cooling Loop

40 min read

Walkthrough — Design a Turbomachinery Cooling Loop

A complete, end-to-end engineering walkthrough for sizing and specifying a closed-loop water/glycol cooling system for a 5 MW industrial centrifugal compressor train in process-gas service (refinery / petrochemical plant). This note exercises the engineering library: thermodynamics, fluid mechanics, heat transfer, turbomachinery, materials, controls, codes, and project management. Every paragraph wiki-links the relevant Tier 1, 2, or 3 reference note so the reader can drill down on any specific topic.

The reader is assumed to be a process / mechanical engineer doing FEED (front-end engineering design) on a new compressor installation, or a retrofit of an existing cooling loop. Numbers throughout are realistic for a single-train 5 MW machine — scaling up to multi-train operation is a straightforward area-and-flow multiplication.

1. What we are building

The compressor under cooling is a single-casing, three-stage centrifugal compressor delivering process gas (e.g., propane + ethane mix to a depropanizer overhead, or recycle hydrogen on a hydrocracker) at approximately 5000 kW (5 MW, 6700 hp) shaft input. The machine geometry is per [[Engineering/pumps-turbomachinery]] and [[Engineering/Tier3/pumps-taxonomy]] (rotor dynamics, head coefficient, surge margin). The driver is a synchronous electric motor or a steam-turbine; either way the heat-rejection scope is the same: take heat out of the lube-oil, the gas between compression stages, and the dry-gas seal panel, and reject it to ambient.

Heat-rejection budget (Q_reject):

SourceDuty (kW)Source temperatureNotes
Lube-oil cooler15075°C oil → cool to 50°CAPI 614 lube system
Inter-stage gas cooler1200gas 120°C → cool to 50°Cbetween stage 1 and stage 2
Seal-gas conditioning5080°C → 35°Cdry-gas-seal supply panel
Total Q_reject1400 kW (1.4 MW)~28% of compressor shaft power

The coolant is a 30% propylene glycol (PG) + 70% water mixture — food-safe (in case of accidental leak into a process stream containing food-grade naphtha or ethylene cracker feed), and freeze-protected to about −10°C. Propylene-glycol chemistry is summarized in [[Engineering/Tier3/refrigerants]] (heat-transfer fluids section).

Loop temperatures, the design ΔT:

  • T_in_to_user (cold supply) = 32°C (90°F)
  • T_out_of_user (warm return) = 42°C (108°F)
  • ΔT = 10°C (18°F)

Using the energy balance from [[Engineering/thermodynamics]] (first law for an open system at steady state), Q = m_dot × cp × ΔT. With cp = 3850 J/(kg·K) for 30% PG at 35°C bulk mean:

m_dot = Q / (cp × ΔT) = 1.4 × 10^6 / (3850 × 10) = 36.4 kg/s ≈ 130 m³/h ≈ 572 USgpm

System operates 24/7/365 with a 99.5% uptime requirement (≈ 44 hours per year planned outage allowance) — typical for refinery service in a continuous process unit. This drives a heavy bias towards redundancy, robust mechanical seals, and N+1 instrumentation.

2. Thermodynamics + fluid first-cut

Before sizing any hardware we close the global energy balance, the global mass balance, and check the freeze-protection requirement against the local 100-year minimum dry-bulb temperature. Energy in = energy out at steady state per [[Engineering/thermodynamics]]: 1.4 MW into the coolant equals 1.4 MW out at the tower (less ~1% pump-shaft work which goes in as additional sensible heat — small but not zero, we add it as a 14 kW debit in the tower duty).

Mass in = mass out by [[Engineering/fluid-mechanics]] continuity: the closed loop has zero net mass flow across its boundary except for makeup and bleed at the tower-water side. The closed glycol loop itself is sealed except for breathing through the expansion-tank vent. Makeup glycol consumption is essentially zero except for top-up after maintenance — say 200 L/year.

30% PG fluid properties at 30°C bulk (DOW Chemical / Meglobal datasheet; [[Engineering/Tier3/refrigerants]]):

Property30% PGWaterRatio
Density ρ (kg/m³)10279961.03×
Specific heat cp (J/kg·K)385041800.92×
Viscosity µ (cP)3.50.804.4×
Thermal conductivity k (W/m·K)0.460.620.74×
Prandtl number Pr295.45.4×
Freezing point (°C)−130—

The implications, per [[Engineering/heat-transfer]] and [[Engineering/fluid-mechanics]]:

  • 8% lower cp means 8% higher mass flow for the same Q and ΔT than pure water.
  • 4.4× higher viscosity means significantly higher pumping power: pressure drop scales roughly as ρ·V²·f, and the friction factor at typical Re ≈ 80 000 in a 6” pipe stays in the turbulent regime but rises ~15% versus water.
  • 0.74× thermal conductivity plus lower Re lowers the heat-transfer coefficient h on tube/plate surfaces by roughly 25%, increasing required HX area.
  • Pr = 29 is materially higher than water; correlations like Dittus-Boelter (h·D/k = 0.023·Re^0.8·Pr^0.4 for heating) reflect this.

Net penalty for glycol vs water: about 20-30% larger pump, 15-20% larger HX. Worth it for freeze protection because the cost of a single freeze-burst on an outdoor air-cooler header is catastrophic ($500k repair + lost production).

3. Heat-rejection sink — option study

The 1.4 MW (and we add 7% design margin → call it 1.5 MW design duty) has to go somewhere — air, water, or once-through. We evaluate three options, per [[Engineering/heat-transfer]] and [[Engineering/hvac-fundamentals]]:

Option (a): Air-cooled fin-fan heat exchanger (ACHE). Direct rejection of the glycol loop to ambient air with no intermediate water side. Hudson Products / Chart / SPX-Hamon type tubular ACHE per API 661, e.g., the Hudson Tubular series. For 1.5 MW at 38°C design ambient → 60°C peak hot-day, with glycol 42°C inlet → 32°C outlet, the LMTD is poor (~10 K average), driving large area: ~700 m² of finned area, four bays of 25-hp fans (each ~19 kW shaft, four bays ≈ 75 kW total fan power), forced-draft. No makeup water, low water-treatment cost, but fan power is high and footprint is large (~10 m × 6 m). Cost installed $200-300k. Reference materials and tube selection in [[Engineering/Tier3/heat-transfer-correlations]] (compact-HX section) and [[Engineering/Tier3/copper-alloys]] (admiralty-brass fin tubes).

Option (b): Closed-loop cooling tower + plate heat exchanger. Wet cooling tower (induced-draft cross-flow or counter-flow) circulates open cooling water through a plate heat exchanger (PHE), which in turn cools the closed glycol loop. The tower can be open (cooling water in direct air contact in the fill) with a closed PHE separating from the dirty glycol, or closed (cooling water also in a closed loop inside the tower, with sprayed water outside the coils — Baltimore Aircoil-style closed-circuit cooler). We pick the open tower + plate HX combination — proven, cheap, easy to clean. Per [[Engineering/hvac-fundamentals]] psychrometric analysis (next section), at 27°C wet-bulb design and 5°C approach, we get 32°C cold water — exactly our 32°C glycol-supply target after a 0°C “approach” across the PHE (in practice add 2°C: glycol supply 34°C, cooling-tower cold water 32°C). Fan power 75 kW total. Makeup water ~4 m³/h. Cost installed $150-250k.

Option (c): Once-through river/seawater cooling. Only viable where water rights and discharge permits allow — e.g., coastal refineries with a marine cooling-water network. Pulls seawater through coarse screens, fish-protection, chlorination injection (NaOCl 1-2 ppm residual), then through titanium-tube plate exchanger (Ti grade 1 or 2 per [[Engineering/Tier3/titanium-alloys]]) with Ni-Al-bronze (C95800) tubesheet per [[Engineering/Tier3/copper-alloys]]. Initial cost is high (Ti plates 3× cost of 316SS), but no tower fans, no makeup chemistry. Discharge temperature must stay within permit limits (typically +5-7°C delta over intake) — at 1.5 MW that requires 200-250 m³/h seawater flow.

Choice: Option (b) — closed-loop cooling tower with intermediate plate HX. Reasons: water available at site, mild climate, well-understood maintenance, lowest fan power, best winter-operation flexibility (can throttle tower in cold months). The remainder of the walkthrough builds on this choice.

4. Cooling-tower sizing

The cooling tower is the heart of the heat-rejection sink. We use a counter-flow induced-draft (ID) tower with PVC film fill, e.g., Marley NC-class, EVAPCO AT, or SPX SPX-class. Sized to the local design conditions per [[Engineering/hvac-fundamentals]] (psychrometrics) and the CTI ATC-105 standard.

Design ambient:

  • Wet-bulb 27°C (1% exceedance, ASHRAE Fundamentals Handbook for Gulf-Coast/Houston area)
  • Dry-bulb 38°C
  • Relative humidity at design ≈ 50%

Tower duty:

  • Range = T_hot_water − T_cold_water = 42°C − 32°C = 10°C (the cooling-water side range matches the PHE process side)
  • Approach = T_cold_water − T_wet_bulb = 32°C − 27°C = 5°C (tight; standard practice is 4-7°C)
  • Capacity = 1.5 MW (1.07× design margin over 1.4 MW Q_reject), or 1500 kW

In conventional cooling-tower units this is a duty factor of ≈ 1.5 MW / (10 K × 4.18 kJ/kg·K) = 36 kg/s = ~129 m³/h cooling-water flow — matched to our glycol-side flow (by design — equal ΔT across the PHE gives a balanced thermal duty and minimizes plate area).

Tower physical size:

  • PVC film fill (e.g., Brentwood Industries XF150 or 2H AF1200): ~200 m² plan footprint × 3 m fill depth
  • Drift eliminators: cellular PVC drift eliminator (Brentwood XCEL), drift < 0.005% of circulated flow
  • Fan: two-cell ID, one 50 hp (37 kW) two-speed or VFD-driven axial fan per cell → 75 kW total when both at full speed, scales down quadratically with airflow per affinity laws [[Engineering/pumps-turbomachinery]]

Makeup water budget:

  • Evaporation E ≈ Q / (h_fg × ρ_water) = 1.5 × 10^6 / (2.4 × 10^6 × 1000) = 0.625 × 10^−3 m³/s = 2.25 m³/h
  • Drift D = 0.005% × 130 m³/h = 0.0065 m³/h (negligible)
  • Bleed B = E / (CoC − 1) where CoC = cycles of concentration; at CoC = 4, B = 2.25 / 3 = 0.75 m³/h
  • Total makeup ≈ E + B ≈ 3 m³/h (4 m³/h with 30% design margin)

Water treatment (Nalco / Veolia-Suez / ChemTreat scheme — see [[Engineering/hvac-fundamentals]]):

  • Corrosion inhibitor: sodium molybdate (Na₂MoO₄) 100-200 ppm + tolyl-triazole 5 ppm for yellow-metal protection
  • Scale inhibitor: HEDP (1-hydroxyethylidene-1,1-diphosphonic acid) 10-15 ppm
  • Biocide: alternating oxidizing (NaOCl to 0.5 ppm free Cl₂) and non-oxidizing (isothiazolinone)
  • pH 8.5-9.0 maintained by acid feed (H₂SO₄ 93%) if alkalinity high
  • Conductivity max 2000 µS/cm → bleed valve modulated on conductivity controller (more on this in section 13)
  • Legionella mitigation per ASHRAE 188-2018 (next-to-section 21)

5. Plate heat exchanger (cooling-tower interface)

The plate HX sits between the closed glycol loop and the open cooling-tower water. It is the thermal bottleneck of the system — get it wrong and either flow regime starves. We size per [[Engineering/Tier3/heat-transfer-correlations]] and per Alfa Laval / Kelvion / SPX product engineering charts.

Selection: Alfa Laval M10-BFG, 180-plate, gasketed plate-and-frame.

  • Plates: AISI 304 stainless steel, herringbone (chevron) pattern, 0.5 mm thickness — per [[Engineering/Tier3/stainless-steels]]
  • Gaskets: EPDM peroxide-cured, 105°C continuous, glued (clip-on optional for field service) — per [[Engineering/Tier3/seals-taxonomy]]
  • Frame: carbon-steel epoxy-painted, ASME B16.5 Class 150 nozzles, 4” inlet/outlet both sides

Thermal sizing — quick BoE:

LMTD with the two sides countercurrent and matched 10 K ranges:

  • Side A (glycol): 42°C in / 32°C out
  • Side B (cooling water): 32°C in / 42°C out (sic — counter-flow gives 32 vs 42 at the cold end)

Wait — that’s not physical. The cold-end driving force must be > 0. Let’s redo with the PHE actually putting cooling water (cold) against glycol (hot):

  • Hot side (glycol return from compressor users): 42°C in / 32°C out (cools)
  • Cold side (cooling-tower cold supply): 32°C in / 42°C out (warms) — at matched flow and matched cp this is balanced
  • Approach at cold end: 32°C glycol exit vs 32°C cooling-water entry → 0°C — infeasible LMTD

So in practice we run an asymmetric ΔT: cooling-tower cold water at 30°C, glycol cooled to 32°C → cold-end approach = 2°C. Tower then has to do 30°C cold water at 27°C WB → 3°C approach. Tighter, larger tower (or accept 34°C glycol supply and re-spec downstream coolers).

Let’s keep glycol supply at 32°C and accept a tower cold-water of 30°C, range 8°C (instead of 10°C). New tower cooling-water flow: m = Q / (cp × ΔT) = 1.5e6 / (4180 × 8) = 45 kg/s (162 m³/h instead of 130). Larger tower-side pump, larger tower fill — but the PHE works.

Revised LMTD:

  • Hot end: glycol 42°C / CW 38°C → ΔT_hot = 4°C
  • Cold end: glycol 32°C / CW 30°C → ΔT_cold = 2°C
  • LMTD = (4 − 2)/ln(4/2) = 2/0.693 = 2.9°C ≈ 3 K

UA required: Q / LMTD = 1500 / 2.9 = 517 kW/K Area required: with overall U ≈ 4000 W/m²·K typical for water-glycol in a PHE (Pr-corrected from a clean-water 5000-6000 baseline), A = 517 000 / 4000 = 130 m²

We had originally targeted 56 m² assuming LMTD = 5 K. The 3 K LMTD doubles it. Lesson: matched-flow PHE design with both 10°C ranges runs into a vanishing pinch-point. Either accept asymmetric ΔT, or relax the glycol supply spec, or accept double the PHE area. We go with double the PHE area: Alfa Laval M15-BFG, 280-plate, total area ~130 m². Cost up to $90-110k.

Pressure drop ~30 kPa per side at rated flow — within pump head budget.

6. Pumps — primary and secondary

Two pump trains: (i) primary closed-loop glycol circulation pump, (ii) cooling-tower water circulation pump. Both end-suction single-stage centrifugal per API 610 (heavy-duty process) — in practice ANSI B73.1 horizontal end-suction is more typical for utility duty in this size and is what we spec, per [[Engineering/pumps-turbomachinery]] and [[Engineering/Tier3/pumps-taxonomy]].

(i) Primary glycol-circulation pump:

  • Flow Q = 130 m³/h (572 USgpm)
  • Head H = 35 m (sum of: HX losses 12 m + piping friction 8 m + control-valve drop 6 m + elevation 4 m + safety margin 5 m)
  • Hydraulic power P_h = ρ·g·Q·H = 1027 × 9.81 × 0.036 × 35 = 12.7 kW
  • Pump efficiency at BEP for this size ~ 72%: shaft P = 12.7 / 0.72 = 17.6 kW
  • Plus drive losses / margin: 25 kW shaft, motor 30 kW with 1.15 SF — round to 30 kW motor, 4-pole 1480 rpm
  • Selection: Goulds 3196 STX size 3x4-10 with 240 mm impeller, or Sulzer ZE 80-200 — both ANSI B73.1
  • Material: ductile-iron casing (ASTM A536 65-45-12), 316SS impeller (cleaner than CF8M cast equivalent), 316SS shaft sleeve — per [[Engineering/materials-steel]]
  • VFD: ABB ACS880-01-061A-3 or Siemens SINAMICS G120 with 30 kW rated — see section 14

NPSH check:

  • Tank vented at atmospheric P_atm = 10.3 m (sea-level)
  • Tank static head above pump centerline = +2 m
  • Friction in suction piping (10 m of 6” pipe, two elbows, one valve) ≈ 1 m
  • Vapor pressure of 30% PG at 30°C ≈ 0.031 bar = 0.31 m
  • NPSH_available = 10.3 + 2 − 1 − 0.31 = 11.0 m
  • NPSH_required (from pump curve at BEP) ≈ 4 m
  • NPSH margin = 7 m — comfortable; no cavitation risk
  • Cross-reference: cavitation theory in [[Engineering/fluid-mechanics]] and [[Engineering/pumps-turbomachinery]]

(ii) Cooling-tower water pump:

  • Flow Q = 162 m³/h (713 USgpm)
  • Head H = 25 m (PHE 4 m + tower riser 8 m + return piping 6 m + tower distribution 4 m + margin 3 m)
  • Shaft P ≈ 14 kW; motor 22 kW with 1.5 service-factor margin for slop, 22 kW motor
  • Selection: ITT Goulds 3175 8x10-12 or Sulzer A22-100, cast iron casing + bronze impeller (cooling-water service tolerates Cu alloy contact)
  • Cast iron A48 / bronze C90500 wetted parts — per [[Engineering/Tier3/copper-alloys]]

Mechanical seals (API 682 4th ed):

  • Glycol-side pump: API 682 Plan 11 (recirculation from discharge through orifice back to seal chamber to flush + cool the seal faces) — clean closed-loop fluid. Single-cartridge balanced seal, carbon-vs-silicon-carbide faces, FKM (Viton) elastomers — per [[Engineering/Tier3/seals-taxonomy]]
  • Cooling-water-side pump: API 682 Plan 23 (with seal cooler — small shell-tube on a closed-loop recirculation around the seal) — water can have suspended solids and tower drift, the cooler keeps face temperature stable. Same materials (SiC/carbon, FKM).

Redundancy: 1+1 configuration each side — one operating, one standby. Auto-changeover on low-flow / high-vibration / high-seal-temperature trips → see section 13 SIS logic and [[Engineering/reliability-engineering]].

7. Pipe sizing — primary loop

The primary glycol loop carries 130 m³/h at design. Target velocity in the main header per [[Engineering/hydraulics-pipe-networks]] and Crane TP-410 is 2.0-3.0 m/s for cooling-water service — high enough to flush sediment, low enough to keep friction reasonable.

Diameter calculation:

  • D = √(4Q / πV) where V = 2.5 m/s and Q = 0.036 m³/s
  • D = √(4 × 0.036 / (π × 2.5)) = √(0.0184) = 0.136 m = 136 mm
  • Closest NPS: 6” Schedule 40 carbon steel (ID 154.1 mm = 6.07”)
  • Actual V at 6” Sch 40: V = Q / A = 0.036 / (π × 0.077²) = 0.036 / 0.0186 = 1.93 m/s ✓ (well within target)

Pipe material specification:

  • ASTM A106 Grade B seamless carbon steel for service per [[Engineering/Tier3/pipe-fittings]] and [[Engineering/Tier3/steel-grades]]
  • Schedule 40 (wall 7.11 mm at 6” NPS); design pressure 16 bar, design temp 80°C
  • Buttweld fittings A234 WPB, ASME B16.9 — long-radius elbows preferred for low pressure drop
  • Flanges ASME B16.5 Class 150 raised-face, 3/16” spiral-wound stainless gaskets with flexible-graphite filler

Friction-loss calculation — Darcy-Weisbach (per [[Engineering/fluid-mechanics]]):

  • Re = ρVD/µ = 1027 × 1.93 × 0.154 / (3.5e-3) = 87 200 (turbulent)
  • ε/D = 0.046 mm / 154 mm = 0.000299 (commercial carbon steel)
  • From Moody chart: f = 0.022
  • Equivalent length L_eq for entire loop: 60 m straight pipe + 12 LR-elbows × K=0.3 = 12 × 7.7 = 92 m equivalent + 2 gate valves K=0.15 = negligible + 2 check valves K=2 = 2 × 51 = 102 m equivalent = total ~250 m equivalent
  • ΔP_friction = f × (L/D) × ρV²/2 = 0.022 × (250/0.154) × 1027 × 1.93² / 2 = 0.022 × 1623 × 1912 = 68 300 Pa = 68 kPa = 6.9 m of glycol head

Plus equipment drops: PHE 30 kPa + lube cooler 25 kPa + inter-stage cooler 40 kPa + seal-gas cooler 15 kPa + control valve 60 kPa (sized for authority — see section 8) = 170 kPa = 17.3 m of glycol head.

Total system head: 6.9 + 17.3 = 24.2 m hydraulic + 4 m elevation + 5 m margin = ~33 m. Matches our pump pick of 35 m at BEP — good.

8. Valves — isolation, throttling, safety relief

Valve selection per [[Engineering/Tier3/valves-taxonomy]] and Velan / Crane / Fisher catalogs.

Main isolation gate valves

  • Velan F02-3074C or Crane K-Flo K-103 Class 150 cast-steel WCB (ASTM A216) flanged gate valve at each end of each pump train, at the PHE, and at every cooler. Bidirectional, low pressure drop (Cv ≈ 1200 for a 6” gate valve at full open), full-port, OS&Y rising-stem with bolted bonnet.
  • Used for isolation only — never throttle a gate valve (seat erosion + flow-induced vibration).

Butterfly valves on bypass and balance lines

  • Bray Series 31 resilient-seated butterfly, lug body, Class 150 — for bypasses, balance lines, and tower-cell isolation.
  • 6” Cv ≈ 720 at full open. Used for coarse manual balance and as a tertiary isolation device.

Check valves

  • DFT Inc. PDC dual-plate (twin-disc) check valve Class 150, 6” — short face-to-face length, low cracking pressure (~0.3 psi), spring-loaded, prevents reverse flow on pump trip.
  • Loss coefficient K=2 (used in section 7 above), Cv ≈ 480.

Control valve — cooling-tower water flow modulation

  • Fisher EZ globe valve, 4”, Class 150 — linear trim, equal-percentage characteristic not needed (process is approximately linear-gain), rangeability 30:1.
  • Cv sizing (per ISA 75.01 / ANSI/FCI): at rated 162 m³/h cooling water and 60 kPa drop, Cv_required = Q × √(SG / ΔP_psi) = 713 × √(1.0 / 8.7) = 713 / 2.95 = 242 at full open.
  • Actual full-open Cv of 4” EZ globe = ~250 — fits with no margin to spare; uprated to 6” EZ Cv 950 to get 4× rangeability margin (control-valve authority > 50% of system ΔP).
  • Pneumatic diaphragm actuator + Fisher FieldVue DVC6200 HART digital positioner; air-fail-open (FO) action on the bleed (we want to dump heat under failure) or air-fail-close (FC) on tower-water bypass (we want to keep cooling flowing).

Safety relief valve

  • Crosby JOS-E spring-loaded RV, 2” × 3” flanged, Class 150 inlet/outlet, set pressure 10 bar g, located at the discharge of the primary glycol pump (protects against deadheaded pump, thermal expansion in trapped sections).
  • Sized per API 520 / ASME BPVC VIII for 1.5× rated pump flow on closed-valve scenario — i.e., 195 m³/h at 10 bar. Capacity per nameplate ~ 250 m³/h water-equivalent — ample.
  • Discharge to drain header back to expansion tank (no atmospheric release of glycol).

Manual ball valves, vents, drains

  • 3/4” Class 150 forged-steel 2-piece ball valves (Velan B05) at all instrument taps, all high points (vent), all low points (drain).

9. Tank, expansion + makeup

The closed glycol loop needs an expansion volume to absorb the thermal expansion of the fluid as it cycles from cold standby (20°C) to operating warm (45°C average bulk). Glycol thermal expansion coefficient β ≈ 6 × 10^−4 / K. With 12 m³ total system volume and ΔT = 25°C, expansion = V × β × ΔT = 12 × 6e-4 × 25 = 0.18 m³ = 180 L. Plus 50% margin and 1 m³ working volume → 5 m³ atmospheric expansion tank (1.5 m diameter × 3 m tall, vertical, conical bottom).

Tank specifics:

  • Material: 304SS or carbon-steel with internal epoxy lining (Belzona 1391S) — per [[Engineering/Tier3/stainless-steels]] and [[Engineering/materials-steel]]
  • Vented through condensate trap (PVC trap with water seal) to atmosphere — keeps loop at atmospheric reference
  • Optional N₂ blanket via Linde NitroFill blanket regulator (0.1 bar above atmospheric, dry nitrogen feed) to suppress dissolved-oxygen pickup and resulting glycol oxidation to glycolic / formic acid (which would lower pH and accelerate corrosion). N₂ supply from plant header or dedicated PSA generator.
  • Emergency makeup tank: 1 m³ HDPE day-tank with manual-isolation top-up line, connected via 1” line and a chemical-metering pump (LMI / Prominent) for periodic glycol replenishment.
  • Mounted above the pump suction: top liquid level at +6 m above pump centerline, providing positive static head and NPSH headroom (calc in section 6).

Air separator:

  • Spirovent VJR or Taco 4900 air separator installed at high point of system on pump discharge — coalescing-element type removes entrained / dissolved air from glycol stream. Air rises to top, gets vented through automatic float-vent. Critical for HX heat-transfer performance (air pockets in tubes → blocked flow → fouling).

10. Pump system curve + part-load operation

Pump and system must intersect at or near BEP. System curve per [[Engineering/pumps-turbomachinery]] and [[Engineering/hydraulics-pipe-networks]]:

H_system(Q) = H_static + (K_total) × Q² / (2g × A²)

where H_static = 4 m (elevation) and K_total is the sum of all loss coefficients including straight pipe (f·L/D) and components. At rated 130 m³/h we calculated H_system = 33 m; at zero flow it’s 4 m; the curve is parabolic between.

Operating-point matching:

  • Pump curve (Goulds 3196 STX, 240 mm impeller, 1480 rpm): H(Q) ≈ 38 − 0.15·(Q/100)² m
  • At Q = 130 m³/h: H_pump = 38 − 0.15 × 1.69 = 37.7 m
  • At Q = 130 m³/h: H_system = 4 + 29 × (130/130)² ≈ 33 m
  • Pump operates slightly to the right of BEP — efficiency drops from 72% to 70%, acceptable
  • Adjust by trimming impeller to 235 mm next overhaul, or rely on VFD throttling

Affinity laws ([[Engineering/pumps-turbomachinery]]):

  • Q ∝ N (flow scales with speed)
  • H ∝ N² (head scales with speed squared)
  • P ∝ N³ (power scales with speed cubed)

Part-load winter operation:

  • In winter, wet-bulb drops to 5°C → cold-water from tower could approach 8°C if fans run full speed → glycol supply 10°C, too cold (compressor lube-oil viscosity rises, bearings starved).
  • Strategy: throttle tower fans via VFD on glycol-supply T_set = 30°C, and throttle primary pump via VFD on flow setpoint cascaded from compressor user-side ΔT (target 10°C ΔT across each cooler).
  • At 50% load (cool winter day): Q = 65 m³/h, N = 740 rpm (half speed), H = 8.3 m, P = 2.2 kW (vs 17.6 kW full load) — massive energy savings.
  • Annual VFD savings: ~30% pump-energy reduction × 30 kW × 8000 h = 0.08/kWh.

11. Heat exchangers — process-side units

Three coolers serve the compressor users: lube-oil, inter-stage gas, seal-gas. Each has a distinct duty, geometry, and material spec.

(a) Lube-oil cooler

  • Duty: 150 kW
  • Type: shell-and-tube, TEMA AES (front-end stationary head A, single-pass shell type E, removable rear-head S) — straight tubes, easy mechanical cleaning per [[Engineering/Tier3/pipe-fittings]] and TEMA 10th ed.
  • Geometry: 5 m long × DN 250 (10”) shell × 19 mm (3/4”) OD tubes × 200 tubes, single-pass shell / two-pass tube
  • Tube material: admiralty brass C44300 (70 Cu / 29 Zn / 1 Sn) — fouling-resistant for lube oil with potential moisture pickup; per [[Engineering/Tier3/copper-alloys]]
  • Shell + tubesheet: carbon steel A516 Gr.70
  • LMTD calc: oil 75 → 50°C, glycol 32 → 42°C, counterflow, LMTD = (33 − 18)/ln(33/18) = 15/0.605 = 24.8 K — wait, that’s for the wrong arrangement. Recompute: hot oil 75 (in) and 50 (out), cold glycol 32 (in) and 42 (out), counterflow LMTD: ΔT_hot = 75 − 42 = 33 K, ΔT_cold = 50 − 32 = 18 K, LMTD = (33 − 18)/ln(33/18) = 15 / 0.605 = 24.8 K. Good driving force.
  • Overall U for oil-side fouling ≈ 350 W/m²·K (per [[Engineering/Tier3/heat-transfer-correlations]])
  • Area required A = Q/(U·LMTD) = 150 000 / (350 × 24.8) = 17.3 m²
  • Tube area per tube: π × 0.019 × 5 = 0.298 m² each; need 17.3 / 0.298 = 58 tubes minimum. We spec 200 tubes (with margin and to fit standard shell pitch) → A_actual ~60 m² with 30% fouling margin — generous, prevents lube-oil over-temp on summer days.

(b) Inter-stage gas cooler

  • Duty: 1200 kW (the dominant load)
  • Type: shell-and-tube TEMA AEU (U-tube bundle, removable for cleaning) for gas service with pressure cycling
  • Process gas in tubes (often higher pressure, smaller volume side), glycol in shell
  • Tube material: 316L stainless for general H₂-bearing hydrocarbon; SS 410 for sulfur-free dry gas; or Inconel 625 if H₂S present (NACE MR0175 sour-service). Match to gas composition per [[Engineering/Tier3/stainless-steels]] and [[Engineering/materials-steel]].
  • Geometry: 8 m long × DN 600 (24”) shell × 25 mm OD U-tubes × 400 tubes (effective 800 thermal lengths)
  • LMTD: gas 120 → 50°C, glycol 32 → 42°C (counterflow) — ΔT_hot = 120 − 42 = 78, ΔT_cold = 50 − 32 = 18, LMTD = (78 − 18)/ln(78/18) = 60 / 1.466 = 40.9 K
  • U for gas-side ~ 250 W/m²·K (low pressure gas tends to have low h)
  • A required = 1.2e6 / (250 × 40.9) = 117 m²
  • Tube area per tube length: π × 0.025 × 8 × 2 (U-tube counts twice) = 1.26 m² each; need 117 / 1.26 = 93 tubes — 400 tubes give A = 504 m², well over with fouling margin.
  • TEMA shell-side baffles (single-segment, 25% cut, spacing 0.5 × D_shell): reduce shell-side ΔP to ~40 kPa.

(c) Seal-gas cooler

  • Duty: 50 kW
  • Type: small skid-mount shell-and-tube, BEM (bonnet-end, U-tube) — compact for skid mounting
  • 304SS throughout (small enough not to need cost-optimized materials)
  • Q small, A ~3 m² — typical 1-2 m unit

All three coolers per [[Engineering/Tier3/heat-transfer-correlations]] for U and Pr corrections, and per ASME BPVC Section VIII Div.1 for pressure-vessel design + nameplate per Section VIII Div.1, with required Joint Efficiency E ≥ 0.85 (full radiography for the high-pressure inter-stage cooler).

12. Instrumentation

All field instruments 4-20 mA HART with intrinsically-safe (IS) barriers (or non-IS depending on area classification — Zone 2/Div 2 typical for non-toxic non-flammable utility glycol; Zone 1/Div 1 around gas coolers in hydrocarbon-handling areas). Multi-vendor list, with Endress+Hauser / Rosemount / Yokogawa / Honeywell coverage typical.

Temperatures (T1-T6, RTDs):

  • Pt100 4-wire Class A elements (Heraeus 32209518, Class A per IEC 60751)
  • 1/4” diameter, 6” insertion thermowell, ASME PCC-2 socket-weld to header
  • Smart Tx: Rosemount 644 HART with auto-loop test, accuracy ±0.05% of span
  • Locations: T1 main glycol supply (to users); T2 main glycol return; T3 lube-oil cooler in+out; T4 inter-stage cooler in+out; T5 seal-gas cooler in+out; T6 PHE both sides + cooling-tower cold supply

Pressures (P1-P5):

  • Rosemount 3051S gauge, 0-10 bar g range, accuracy ±0.04% URL
  • Locations: P1 pump discharge; P2 PHE inlet (both sides); P3 each cooler inlet; P4 expansion tank; P5 RV inlet

Flows (F1-F2):

  • Coriolis mass flow for primary glycol — Emerson Micro Motion CMF200M (4” sensor, 5700 transmitter) — mass flow ±0.1%, density ±0.5 kg/m³, simultaneous T measurement.
  • Magnetic flowmeter for cooling-tower water — E+H Promag W500, 6” — accuracy ±0.2%, no pressure drop, suitable for clean water. Mag-flow chosen over Coriolis on cooling-water side because of lower cost and no need for density.

Level (L1):

  • Expansion tank: E+H Levelflex FMP54 guided-wave radar, 6 m probe, accuracy ±5 mm, HART output
  • Tower-basin: E+H Liquiphant FTL51 vibrating-fork point-level switch (low-low and high-high)

Conductivity (C1):

  • Cooling-tower basin: E+H Conducal CLY11 conductivity transmitter, range 0-5000 µS/cm, used for bleed control (see section 13)

pH (Q1):

  • Cooling-tower basin: E+H Orbisint CPS11D glass pH electrode, 0-14 pH, used for acid-feed control

Vibration (V1-V4):

  • Compressor + pump bearings: Bently Nevada 3500 system or SKF Multilog On-Line, 4-channel proximity probes (radial vibration) + 2-channel keyphasor + 2-channel accelerometers (high-frequency bearing condition)
  • Trip at 50 µm peak-peak radial, alarm at 25 µm; integrated with SIS via 4-20 mA + relay
  • Per [[Engineering/Tier3/valves-taxonomy]] (control-valve section) and [[Engineering/reliability-engineering]]

13. Control system

Plant DCS hosts all regulatory + supervisory control. Options: Emerson DeltaV (the most common in petrochem for greenfield), Yokogawa Centum VP (preferred in Asia), or Honeywell Experion (legacy refining). All three support IEC 61131-3 function-block, ISA-95 batch, and OPC UA gateways.

Control strategies per [[Engineering/classical-control]] and [[Engineering/system-identification]]:

Loop 1 — Glycol supply temperature (master controller)

  • PV: T1 (main glycol supply)
  • SP: 32°C
  • MV: cooling-tower fan speed (VFD via 4-20 mA to ABB ACS580)
  • Type: PI, no derivative (process is slow, thermal mass dominates — thermal time constant ~10-15 min for 12 m³ system)
  • Tuning: P = 1.5 (proportional band 67%), I = 5 min integral; tune by Ziegler-Nichols closed-loop or relay-feedback per [[Engineering/classical-control]]
  • Output split-range: 0-50% MV runs one tower-cell fan up from 0 to full speed; 50-100% MV starts second cell fan and ramps it up — gives 4:1 turndown without cycling cells

Loop 2 — Bleed-off control

  • PV: C1 (basin conductivity)
  • SP: 1800 µS/cm (deadband 100 µS/cm)
  • MV: bleed solenoid valve (on/off) or 4-20 mA modulating bleed valve (preferred)
  • Type: PI; slow time scale (hours), so I = 30 min

Loop 3 — Pump flow / pressure cascade

  • Primary cascade: master PID on flow (F1 Coriolis) SP = 130 m³/h, MV = pump VFD speed
  • Slave cascade: trim with discharge pressure setpoint (P1 SP = 5 bar g) — protects against deadhead in case of valve closure event
  • Anti-windup on integral when at speed limits

Loop 4 — Acid feed (pH control)

  • PV: Q1 (pH)
  • SP: 8.7 (deadband ±0.2)
  • MV: metering-pump stroke or speed (Prominent gamma/4)
  • Type: PI, slow (I = 20 min) — pH lag dominates

SIS — Safety Instrumented System (separate from DCS, per IEC 61511 SIL 2):

  • HW: HIMA HIMax F60 or ICS Triplex Trusted T8 or Siemens S7-410F (logic solver), redundant (2oo3 or 1oo2D voting)
  • Trip 1: high bearing temp (Pt100 trip 95°C, 2oo3 vote across three sensors) → trip compressor + glycol pump
  • Trip 2: low glycol flow (Coriolis F1 < 50% of normal for 30 s) → trip compressor (loss of cooling)
  • Trip 3: high pump vibration (Bently Nevada > 50 µm peak-peak) → trip pump, alarm only on compressor side (let operator decide)
  • Trip 4: low expansion-tank level (Levelflex < 20%) → alarm at 30%, trip at 15% (loss of glycol → loss of cooling capability)
  • SIL verification per IEC 61511 — required PFD_avg ≤ 1e-2 (SIL 2). LOPA (Layer of Protection Analysis) documents the credit taken for SIS per [[Engineering/reliability-engineering]].

HMI:

  • Two 27” 4K monitors per operator console; ISA-101 graphic standards (grey backgrounds, no flashing red — only abnormal-state highlighting)
  • Trends 24-hour rolling for all key PVs, 30-day historian (OSIsoft PI, AVEVA Historian, or Honeywell Uniformance)
  • Alarms rationalized per ISA-18.2: each alarm has cause, consequence, response, time-to-act; alarm flood prevention via prioritization

14. Power & VFD

The cooling-loop electrical scope:

MCC (Motor Control Center):

  • 480 V 3-phase 60 Hz (US) or 400 V 50 Hz (Europe), Form 4b per IEC 61439 (separation between busbar, functional unit, terminals, cable connections)
  • Vendor: Eaton Magnum MCC, ABB MNS, Siemens Sivacon, Rockwell CENTERLINE — all options
  • Bucket sizes: 30 kW + 22 kW + 37 kW (tower fans 2 × 37 kW combined) + smaller (acid pump, makeup pump) = 7 buckets typical
  • Short-circuit rating: 50 kA at 480 V — sized for upstream transformer fault current

VFDs (Variable Frequency Drives):

  • ABB ACS880-01-061A-3 (30 kW) for primary glycol pump — integrated common-mode filter, dV/dt filter for long motor leads (>30 m runs)
  • ABB ACS880-01-049A-3 (22 kW) for cooling-tower-water pump
  • ABB ACS580 (37 kW each, 2 units) for tower fan motors
  • All VFDs have built-in PID, communicates with DCS via Profibus DP or Profinet / EtherNet/IP — see comms section

Motors:

  • Premium efficiency IE3 (NEMA Premium) or IE4 (super-premium) per IEC 60034-30-1 and DOE 2010 regs
  • TEFC enclosure (totally enclosed fan-cooled) for outdoor service
  • Class F insulation, Class B rise — gives 25 K thermal margin
  • Bearings: shielded ball at NDE, insulated at DE (VFD-driven motors require shaft-grounding ring or insulated bearing to prevent bearing currents — per [[Engineering/Tier3/electric-motor-taxonomy]])

Harmonics + power quality:

  • Each VFD adds 5th, 7th, 11th, 13th order harmonics on the supply side. Per IEEE 519-2014, total harmonic current distortion (TDD) at PCC must be < 5% for typical industrial supplies.
  • Mitigation: 5% line reactor at each VFD input (passive), or active front end (regenerative VFD — costlier but cleaner). DC-link capacitors per [[Engineering/Tier3/passive-components]] smooth the DC bus.

Auxiliary loads:

  • Heat-trace circuits (Thermon FreezGuard self-regulating cable, 10 W/m at 10°C, 230 V single-phase) on outdoor pipework — total ~5 kW, fed from MCC via thermostat-controlled contactor.
  • Control-panel UPS: 5 kVA Eaton 9PX online double-conversion, 30 min runtime — keeps DCS + SIS alive during ride-through events.

15. Codes and standards

Engineering and procurement are governed by an interlocking stack of codes and standards. The applicable list per [[Engineering/Tier3/engineering-codes]] and [[Engineering/Tier3/standards-bodies]]:

StandardCoverage
ASME B31.3-2022Process piping (this is the master mechanical piping code)
ASME BPVC Section VIII Div.1-2023Pressure vessels (expansion tank, shell-tube coolers)
ASME B16.5-2020Pipe flanges and flanged fittings
ASME B16.9-2018Factory-made buttweld fittings
ASME PCC-2Repair of pressure equipment and piping
API 610 12th edCentrifugal pumps for petroleum, petrochemical and natural-gas industries
API 682 4th edMechanical seals for pumps
API 661 7th edAir-cooled heat exchangers
API 614 5th edLubrication, shaft-sealing, and oil-control systems
API 670 5th edMachinery protection systems
TEMA 10th edStandards of the Tubular Exchanger Manufacturers Association
ANSI/HI 9.8Hydraulic Institute pump intake design
ANSI/HI 14.6Rotodynamic pumps for hydraulic performance acceptance tests
ANSI/ISA 75.01Flow equations for sizing control valves
ANSI/ISA 18.2Management of alarm systems
ASHRAE 90.1-2022Energy standard for buildings (efficiency reqs)
ASHRAE 188-2018Legionellosis: risk management
CTI ATC-105Cooling Technology Institute, thermal performance acceptance test
IEC 61511Functional safety — safety instrumented systems for the process industry
IEC 61882Hazard and operability studies (HAZOP)
NACE MR0175 / ISO 15156Materials for use in H₂S-containing environments
IEEE 519-2014Harmonic control in electric power systems
IEC 60034Rotating electrical machines
Crane TP-410Flow of fluids through valves, fittings, and pipe

Local jurisdiction adds national / state codes — e.g., ASME State Boiler & Pressure Vessel Inspectors registration in the US, PED (Pressure Equipment Directive 2014/68/EU) in Europe, China Manufacture License of Special Equipment (MLSE) in China.

16. Corrosion and materials

Glycol-loop degradation chemistry:

Propylene glycol oxidizes over time in the presence of dissolved oxygen (sucked through breather vents, dissolved during makeup) to form glycolic acid, formic acid, and lactic acid — all of which lower pH and accelerate corrosion. To suppress this:

  • pH monitoring (Q1 sensor, section 12) maintained 8-10
  • Buffer + corrosion inhibitor package: sodium nitrite (NaNO₂) 500-1500 ppm + sodium borate buffer + tolyltriazole 50 ppm (for yellow metals: brass, copper). Commercial product: Dynalene FP30 inhibited, or Dow Dowfrost HD.
  • Annual fluid sampling and lab analysis (glycol concentration, pH, inhibitor residual, dissolved-metal levels) — typical lab Nalco / Sentinel Performance Labs / ChemTreat
  • Inhibitor replenishment every 12-18 months; full glycol-fluid change-out every 5-7 years

Materials selection summary (per [[Engineering/materials-steel]], [[Engineering/Tier3/stainless-steels]], [[Engineering/Tier3/copper-alloys]], [[Engineering/Tier3/steel-grades]], [[Engineering/Tier3/surface-treatments]]):

ComponentMaterialJustification
Main piping (glycol)A106 Gr.B carbon steel, Schedule 40Cheap, code-accepted, inhibited glycol protects
Main piping (cooling water)A106 Gr.B carbon steel + epoxy lining + cathodic protectionResists chloride + dissolved O₂
Expansion tank304SS or epoxy-lined CSCleanliness + glycol compatibility
PHE plates304SSStandard for cooling-water duty
Shell-tube tubes (lube-oil)C44300 admiralty brassFouling resistance
Shell-tube tubes (gas cooler)316L SS or Inconel 625Per process compatibility
Shell-tube shellA516 Gr.70 carbon steelCode-standard pressure vessel
Tube sheetsA350 LF2 or 90/10 CuNi (C70600)Match to tube alloy
Pump casing (glycol)A536 ductile iron or A216 WCB CSStandard ANSI B73.1
Pump impeller (glycol)316SSBetter than CF8M cast for clean glycol
Pump casing (CW)Cast iron + bronze impellerStandard tower-water service
Mechanical-seal facesSilicon carbide vs carbonPer [[Engineering/Tier3/seals-taxonomy]]
Gaskets (PHE)EPDM peroxide-cured110°C continuous, glycol-compatible
Gaskets (flange)Spiral-wound 304SS + flexible graphiteASME B16.20

Galvanic compatibility:

  • Avoid direct contact between carbon steel and 90/10 CuNi — galvanic potential ~250 mV → CS would corrode preferentially.
  • Use insulating lap-joint stub-ends with full-face dielectric gaskets at any CS-to-Cu interface.

17. Insulation + freeze protection

Outdoor pipework needs:

  1. Thermal insulation to keep heat in (loop is 32-42°C, only marginally above ambient, but reduces summer over-temp).
  2. Personnel protection for hot lines (the inter-stage gas cooler runs at 120°C process side — accessible touch-temp must be < 60°C per ASTM C1055).
  3. Freeze protection for any outdoor section that could stagnate.

Insulation system per [[Engineering/heat-transfer]]:

  • Mineral-wool pipe insulation: Rockwool ProRox PS 960 (rigid section), 50 mm thickness on 6” pipe, k = 0.040 W/m·K at 50°C mean
  • Vapor barrier: 50 µm self-adhesive aluminum-foil-reinforced kraft (Knauf Insulation FaceVap)
  • Outer jacket: 0.6 mm aluminum sheet with stainless-steel banding, lap-jointed and sealed with metal-foil tape — UV-resistant, weatherproof for 30+ years
  • Hot-line insulation (inter-stage gas, 120°C): same Rockwool + Al jacket, but with all-welded stainless steel inner liner under the insulation to allow corrosion-under-insulation (CUI) inspection per API 583

Heat-tracing:

  • Thermon FreezGuard FG-5 self-regulating cable, 5 W/m at 10°C, 240 V single-phase
  • Applied as redundancy to freeze protection on outdoor segments — even if circulation stops, heat trace will maintain pipe above the freeze point of the glycol (T_critical = −8°C for 30% PG, but we hold ≥ 5°C as margin)
  • Thermostat: Thermon SES-04 line-sensing thermostat at +5°C cut-in, +10°C cut-out
  • Cable circuits split into 30 m max segments with individual GFI breakers in MCC

Cooling-tower freeze protection:

  • Tower basin heater (immersion electric heater, 5 kW × 4, 240 V single-phase) cycles on at +5°C ambient
  • Tower fan reverse-rotation (jog air upward) during below-freezing operation to prevent fan-blade ice buildup
  • Recirculation valve sends warm water back to basin instead of through fill at low load

18. CFD spot-check

For the highest-flux service item — the inter-stage gas cooler — we run a CFD model to verify hot-spot avoidance, tube-vibration potential, and shell-side flow distribution before committing to manufacture. Per [[Engineering/cfd-deep]] and [[Engineering/Tier3/heat-transfer-correlations]]:

Model setup:

  • Solver: ANSYS Fluent 2024 R2 or OpenFOAM 12 (free option, comparable accuracy with skilled operator)
  • Geometry: 1/4 symmetry of shell + 80 tubes (out of 320 modeled by symmetry × 4) + baffles + nozzles, imported from SolidWorks / NX
  • Mesh: hex-dominant polyhedral, ~20 M cells, y+ < 5 on tube walls (resolved-wall LES not used — too expensive at this Re; we use SST k-ω with wall functions)
  • Turbulence model: k-ω SST (good for separated flow around baffle cuts and impingement on inlet nozzle)
  • Boundary conditions: mass-flow inlet (40 kg/s glycol on shell side), pressure outlet, wall temperatures from tube-pass simulation
  • Energy equation on, conjugate-heat-transfer at tube walls

What we check:

  1. Pressure drop predictions match the Heat Exchanger Institute correlations within 10% — validates the mesh
  2. Cross-flow velocity in the baffle window stays below 1.5 m/s (avoid tube vibration per TEMA E.4.3 / Tinker map)
  3. Inlet nozzle impingement plate sized correctly — local velocity onto the plate < 8 m/s avoids erosion
  4. Hot spots in the tube bundle — identify locations where shell-side glycol velocity drops below 0.3 m/s (deadleg → fouling → local over-temp) and add longitudinal baffles or rotate baffle orientation

A 2-week CFD study (1 week setup + 1 week solve + post) costs ~300k cooler rebuild on first run-in.

19. Cost build-up

ItemCost (USD, 2026 prices)
Cooling tower (installed, including civil pad, electrical, water-treatment skid)$250k
Plate HX (M15-BFG, 130 m², SS304/EPDM)$90k
Pumps (primary + standby + tower-water + standby), motors, VFDs$160k
Piping (6” carbon steel, supports, paint, insulation)$200k
Valves + actuators (Fisher EZ + Velan + DFT + RVs)$120k
Instrumentation (Rosemount/E+H/MicroMotion)$150k
Shell-tube heat exchangers (3 units: lube, gas, seal)$200k
Expansion tank + air separator + makeup pump$40k
DCS integration (DeltaV/Centum/Experion programming + HMI graphics)$200k
Civil + structural (steel skid, foundations, drains)$100k
Commissioning + IO loop check + performance test$120k
Engineering (FEED + detailed design, ~10% of TIC)$150k
Contingency (15%)$200k
TIC (Total Installed Cost)**≈ 1.2-1.6 M depending on location + local labor)

Annual operating cost:

ItemAnnual cost (USD)
Pump + fan electricity (~120 kW average × 8000 h × $0.08/kWh)$77k
Glycol replenishment (5% × 12 m³ × $4/L)$2.4k
Water treatment chemicals (Nalco/ChemTreat program)$20k
Makeup water (4 m³/h × 8000 h × $0.5/m³)$16k
Maintenance (5% of TIC for utilities)$50k
Total annual O&M≈ $165k

Energy cost dominates — that’s why the VFDs pay back: 30% energy savings would save 30k VFD package incremental cost over fixed-speed → 1.3-year payback.

20. Project management

Typical greenfield timeline 12-14 months from sanction to commercial operation per [[Engineering/project-management-engineering]]:

PhaseDurationKey activities
FEED (front-end engineering design)3 monthsP&IDs (revision 0), datasheets, equipment list, MTO, CAPEX ±10%
Detailed design4 months3D model (E3D / SmartPlant / Revit), iso drawings, fab packages, vendor data integration
Procurement(overlaps detailed design)RFQ → bid eval → PO → vendor data → expediting
Long-lead equipment4 monthsCooling tower (CTI-certified), plate HX (Alfa Laval), pumps (Goulds/Sulzer) — these set CPM
Construction + erection4 monthsCivil → mechanical → piping → electrical → instrumentation → insulation
Commissioning + start-up1 monthHydrotest, loop check, dry run, performance test (acceptance per CTI ATC-105 for tower, ANSI/HI 14.6 for pumps)

Schedule tool: Primavera P6 (Oracle, large EPC standard) or Microsoft Project (smaller projects). Critical path runs through cooling tower fabrication (16-week lead time including civil-pad cure) + plate HX (12-week lead). Anything outside that has float.

Cost control: AACE International recommended practice for cost estimation; Class 3 estimate (FEED) ±10%, Class 1 estimate (detailed-design complete) ±5%.

Quality: ASME pressure-vessel U-stamps, Code calculations sealed by registered PE, hydrotest at 1.5× design pressure (24 bar for 16 bar design), NDE (RT or UT) on all welds per B31.3 inspection category D (normal fluid service, 10% RT typical).

HSE: PHA (process hazard analysis) at FEED → HAZOP at detailed design → SIL determination per LOPA → SIS design verification.

21. Risk and safety

HAZOP (Hazard and Operability) study per IEC 61882: scenario-table by node, with deviation guidewords (no flow, more flow, less flow, reverse flow, more pressure, less pressure, etc.). Key findings for this design:

DeviationCauseConsequenceSafeguard
No glycol flowPump trip, valve closure, blockageCompressor over-temp → bearing damage → fireStandby pump auto-start (2-of-2 vote); SIS trip compressor on low flow
Glycol leak in compressor areaHeat-exchanger tube failure, gasket failure, piping ruptureLocal pooling, slip hazard, environmental dischargeCurbing around skid, oil-water separator on drain, sump pump to recovery tank
Loss of cooling towerTower fan trip + power-supply eventGlycol supply temp rises → compressor trip on high bearing temp (SIS)Bypass to ACHE backup (if installed) — not in our design; we rely on SIS-tripped compressor + safe shutdown via dry-gas-seal panel
High glycol pressureDeadhead pump + closed discharge valvePipe burstCrosby JOS-E RV at pump discharge (set 10 bar g), discharge to expansion tank
Legionella contaminationStagnant tower water + biofilm growthPublic-health legionellosis incidentASHRAE 188 program: continuous biocide, monthly bacterial counts, semi-annual cleaning
Glycol contamination of processTube failure in lube-oil cooler (glycol higher pressure than oil)Glycol enters lube system → bearing damagePressure trip on cooler differential; daily sample of lube oil for glycol detection (refractive index trend)

SIL determination (LOPA):

  • Compressor over-temp trip (loss-of-cooling-induced): risk reduction factor (RRF) target = 100 → SIL 1
  • Compressor bearing-vibration trip: RRF target = 1000 → SIL 2
  • Overall SIS bundle design verified per IEC 61511 with vendor TÜV-certified subsystems (HIMA / Triplex)

Fire-and-gas:

  • Hydrocarbon-gas detection (Det-Tronics Eclipse IR3 point IR sensors) around the inter-stage gas cooler (hydrocarbon process gas in tubes) — voted 2oo3 trip on Hi-Hi (40% LEL)
  • Fire detection (Det-Tronics UV/IR3) over the compressor skid — trip to ESD level 1 (compressor + glycol pump + acid feed) on confirmed flame
  • Fire suppression: water deluge (NFPA 15) for compressor skid + dry-chemical (Ansul A-101) on electrical-equipment-only enclosures

Reliability availability maintainability (RAM) target: 99.5% uptime = 44 h/year unplanned outage. From a Markov reliability model per [[Engineering/reliability-engineering]], the dominant unavailability sources are: (i) primary pump MTBF (~25 000 h) with standby switchover failure (~2% probability), (ii) plate-HX gasket leak (~15-year mean), (iii) cooling-tower fan motor (~50 000 h). Target met with 1+1 pumps, semi-annual PHE gasket inspection, and annual fan-motor PdM (vibration + thermography).

22. Cross-reference summary

This walkthrough exercised, in order of appearance, the following library notes:

Tier 1 (foundational):

  • [[Engineering/thermodynamics]] — energy balance, cp, ΔT
  • [[Engineering/heat-transfer]] — conduction, convection, insulation
  • [[Engineering/fluid-mechanics]] — Darcy-Weisbach, NPSH, Re/Pr
  • [[Engineering/pumps-turbomachinery]] — centrifugal pump, BEP, affinity laws, NPSH
  • [[Engineering/hvac-fundamentals]] — psychrometrics, cooling-tower sizing
  • [[Engineering/hydraulics-pipe-networks]] — system curve, K factors
  • [[Engineering/materials-steel]] — carbon-steel + stainless-steel grade selection
  • [[Engineering/classical-control]] — PID tuning, cascade control
  • [[Engineering/system-identification]] — process modelling for tuning
  • [[Engineering/reliability-engineering]] — RAM, MTBF, FMEA
  • [[Engineering/project-management-engineering]] — Primavera, CPM, AACE

Tier 2:

  • [[Engineering/cfd-deep]] — CFD spot-check, k-ω SST

Tier 3 (specialty):

  • [[Engineering/Tier3/heat-transfer-correlations]] — compact-HX U values, Dittus-Boelter
  • [[Engineering/Tier3/refrigerants]] — propylene glycol, water, heat-transfer fluids
  • [[Engineering/Tier3/seals-taxonomy]] — mechanical seals, gaskets
  • [[Engineering/Tier3/stainless-steels]] — 304/316L for PHE plates and small coolers
  • [[Engineering/Tier3/titanium-alloys]] — Ti for seawater service (option c)
  • [[Engineering/Tier3/copper-alloys]] — admiralty brass, CuNi for tubes
  • [[Engineering/Tier3/pumps-taxonomy]] — ANSI B73.1, API 610 selection
  • [[Engineering/Tier3/pipe-fittings]] — A106, B16.5, B16.9
  • [[Engineering/Tier3/steel-grades]] — A516 Gr.70, A350 LF2
  • [[Engineering/Tier3/valves-taxonomy]] — gate, butterfly, check, control valves; Cv sizing
  • [[Engineering/Tier3/electric-motor-taxonomy]] — IE3/IE4, TEFC, shaft grounding
  • [[Engineering/Tier3/passive-components]] — DC-link caps in VFDs
  • [[Engineering/Tier3/engineering-codes]] — ASME, API, NACE, IEC
  • [[Engineering/Tier3/standards-bodies]] — ASME, API, ASHRAE, CTI, IEC, ANSI/HI
  • [[Engineering/Tier3/surface-treatments]] — epoxy lining, cathodic protection

Total: 4 Tier-1, 1 Tier-2, 16 Tier-3 notes consulted in a single integrated design exercise. This is what an integration walkthrough looks like — every back-of-envelope number traces to a referenced principle in the underlying library.

23. Citations

Primary references for numerical and material data used above:

  1. ASME B31.3-2022, Process Piping, American Society of Mechanical Engineers.
  2. ASME BPVC Section VIII Division 1, 2023 ed., Rules for Construction of Pressure Vessels.
  3. API Standard 610, 12th ed. (2021), Centrifugal Pumps for Petroleum, Petrochemical and Natural Gas Industries.
  4. API Standard 682, 4th ed. (2014), Pumps — Shaft Sealing Systems for Centrifugal and Rotary Pumps.
  5. API Standard 661, 7th ed. (2013), Petroleum, Petrochemical, and Natural Gas Industries — Air-Cooled Heat Exchangers.
  6. TEMA Standards, 10th ed. (2019), Tubular Exchanger Manufacturers Association.
  7. ASHRAE Handbook — HVAC Systems and Equipment, 2024 ed., American Society of Heating, Refrigerating and Air-Conditioning Engineers.
  8. ASHRAE 188-2018, Legionellosis: Risk Management for Building Water Systems.
  9. Cooling Technology Institute, CTI ATC-105, Acceptance Test Code for Water Cooling Towers.
  10. Crane Technical Paper No. 410 (TP-410), 2018 ed., Flow of Fluids Through Valves, Fittings, and Pipe, Crane Co.
  11. ANSI/HI 14.6-2022, Rotodynamic Pumps for Hydraulic Performance Acceptance Tests, Hydraulic Institute.
  12. IEC 61511-1/2/3, Functional safety — Safety instrumented systems for the process industry sector.
  13. IEC 61882:2016, Hazard and operability studies (HAZOP studies) — Application guide.
  14. NACE MR0175 / ISO 15156:2020, Petroleum and natural gas industries — Materials for use in H₂S-containing environments in oil and gas production.
  15. ANSI/ISA-75.01.01-2012 (R2018), Industrial Process Control Valves — Flow Equations for Sizing Control Valves.
  16. DOW Chemical / Meglobal DOWFROST HD Engineering and Operating Guide, 2022 revision (propylene-glycol properties).
  17. Alfa Laval product catalog: M-Series Gasketed Plate Heat Exchangers, 2023.
  18. Goulds Pumps (ITT) Model 3196 ANSI B73.1 process pump engineering data, 2024.
  19. Hudson Products Corporation ACHE design manual, 2022.
  20. Bently Nevada 3500 System overview, Baker Hughes Digital Solutions, 2023.

End of walkthrough.

Graph View

Backlinks