equinor NeqSim Utilities Specification Skill
Specify and size the seven core utilities every process plant needs:
steam, cooling water, instrument air, fuel gas, nitrogen, demin water, refrigeration.
Choices are usually decided by the grand-composite curve from neqsim-heat-integration
and constrained by site standards (NORSOK U-001, IOGP S-714).
When to Use
- Consolidating heating/cooling duties into utility headers
- Choosing between utility levels (LP vs MP steam, CW vs chilled water)
- Sizing utility headers and consumers
- Drafting utility design basis for FEED
- ESG / energy intensity reporting (kg CO₂ per t product)
Standards: NORSOK U-001 (utility systems), NORSOK P-002 (utility design), IOGP S-714, ASME PTC 12 (steam quality), ISA-7.0.01 (instrument air).
Utility 1 — Steam (HP / MP / LP)
Typical levels — pick from the grand composite curve:
| Level | Pressure | Saturation T | Service |
|---|---|---|---|
| HP | 40–100 barg | 250–310 °C | Driving steam turbines, high-T reboilers |
| MP | 10–25 barg | 180–225 °C | Reboilers, glycol regen, stripper |
| LP | 3–6 barg | 130–160 °C | Tracing, deaerator, low-T reboilers |
| Atmospheric | 0 barg | 100 °C | Heating coils, tank heating |
Selection rule: pick the lowest level that beats the cold stream by ΔTmin + 10 °C margin. Lower steam = cheaper and lets HP go to power generation.
Sizing inputs:
- Total reboiler / heater duty per level
- Letdown allowance (10–20% spare)
- Network losses (3–5% per km of header)
Boiler / HRSG feed water (BFW):
- Conductivity < 0.3 µS/cm (per ASME PTC 12)
- O2 < 7 ppb (deaerator + scavenger like hydrazine or carbohydrazide)
- Hardness < 0.01 ppm (softener / RO)
Utility 2 — Cooling Water
Q_cool = ṁ_CW × cp × (T_return − T_supply)
| Parameter | Tropical | Temperate | Arctic |
|---|---|---|---|
| T_supply (°C) | 32 | 25 | 10 |
| T_return (°C) | 42 | 35 | 25 |
| ΔT design | 10 | 10 | 15 |
| Cycles of conc. | 4–6 | 5–7 | 5–7 |
| Velocity (tube) | 1.5–2.5 m/s | 1.5–2.5 m/s | 1.5–2.5 m/s |
| Fouling factor | 0.0002 m²K/W | 0.0001 m²K/W | 0.0001 m²K/W |
Pinch on CW: cooler outlet T_process must be ≥ T_supply + ΔTmin (typically 8–10 °C); otherwise switch to chilled water or air cooler.
Air coolers preferred when:
- Site lacks abundant water
- Service T > 60 °C (CW would scale)
- Environmental discharge restricted
Utility 3 — Instrument Air (ISA-7.0.01)
| Specification | Value |
|---|---|
| Pressure | 7–9 barg |
| Dew point | ≤ −40 °C (atmospheric) — keep dry |
| Particulates | ≤ 40 µm |
| Oil content | ≤ 1 mg/m³ |
| Header sizing | Σ users × 1.5 + 25% spare |
| Receiver volume | 5 min @ peak demand |
| Backup | N₂ tie-in for emergency |
Utility 4 — Fuel Gas
For gas turbines, fired heaters, flare pilots:
| Spec | Typical |
|---|---|
| LHV (Wobbe Index variation) | < ±5% of design |
| Pressure (turbine) | 25–35 barg |
| H2S content | < 4 ppmv (NORSOK), < 250 mg/Nm³ (general) |
| Liquid carryover | None — KO drum upstream |
| C5+ dewpoint margin | ≥ 20 °C above lowest pipeline T |
| Heating value | 30–50 MJ/Nm³ for natural gas |
Use NeqSim to build the Wobbe Index calc:
double LHV = fluid.getCombustionEnergy("LHV/MJ/Sm3");
double SG = fluid.getMolarMass() / 28.96;
double WI = LHV / Math.sqrt(SG); // Wobbe index
Utility 5 — Nitrogen
| Service | Purity | Pressure | Notes |
|---|---|---|---|
| Purging / inerting | 99.5% | 7–10 barg | Bulk N₂ ok |
| Blanketing | 99.9% | 0.05 barg | Tank low-P |
| Catalyst regen / sour service | 99.99% | 7 barg | Cryogenic / PSA |
| Instrument backup | 99.5% | 7 barg | Tie-in to IA header |
Volume rule for vessel inerting: 5× geometric volume at atmospheric to reach ≤ 1% O₂.
Utility 6 — Demineralized Water
| Service | Conductivity | Notes |
|---|---|---|
| BFW / HRSG | < 0.3 µS/cm | Mixed-bed polished |
| Chemical injection make-up | < 1 µS/cm | Two-bed sufficient |
| Wash water (GBS, sour) | Drinking water | Cl < 250 ppm |
Utility 7 — Refrigeration (Chilled Water / Propane / Mixed Refrigerant)
When CW can't reach the temperature target:
| Service | Temp range | Refrigerant |
|---|---|---|
| Chilled water | 5–15 °C | NH₃ or absorption chiller |
| Propane | −40 to 0 °C | C3 cycle (LNG, NGL recovery) |
| Cascade / MR | < −40 °C | C3-MR, DMR (LNG) |
| LIN / LHE | < −150 °C | Liquid N₂ / He (specialty) |
For LNG see also neqsim-platform-modeling.
Pattern 1 — Utility Duty Consolidation
double Q_HP_steam = 0, Q_MP = 0, Q_LP = 0, Q_CW = 0, Q_air = 0;
for (ProcessEquipmentInterface eq : process.getUnitOperations()) {
if (eq instanceof Heater) {
double T = ((Heater) eq).getOutletStream().getTemperature("C");
double Q = ((Heater) eq).getDuty();
if (T > 200) Q_HP_steam += Q;
else if (T > 130) Q_MP += Q;
else Q_LP += Q;
} else if (eq instanceof Cooler) {
double T = ((Cooler) eq).getOutletStream().getTemperature("C");
double Q = ((Cooler) eq).getDuty();
if (T > 60) Q_air += Q; // air-cooled
else Q_CW += Q; // CW
}
}
Pattern 2 — Utility Cost Allocation
$/yr = duty × hours × $/kWh
Typical Norwegian indicative numbers (escalate / replace per project):
| Utility | $/MWh |
|---|---|
| HP steam | 25 |
| MP steam | 22 |
| LP steam | 18 |
| Cooling water | 0.5 |
| Air cooling (fans) | 1.5 (electricity only) |
| Refrigeration (propane) | 50–80 |
| Electricity | 70–100 |
Common Mistakes
| Mistake | Fix |
|---|---|
| Single steam level for all heating | At least HP + LP — saves 10–25% energy via pinch |
| CW return T close to wet-bulb | Cooling tower can't approach wet-bulb closer than 3–5 °C |
| Sizing IA at peak demand only | Add 25% spare + receiver for valve-stroke transients |
| Fuel gas spec without Wobbe | Burners care about Wobbe, not just LHV — vary composition tests it |
| N₂ purge based on volume × 1 | Need 4–5 displacements to reach 99% inerting (well-mixed assumption) |
| Demin water spec'd as drinking water | BFW conductivity < 0.3 µS/cm — drinking water is 100–500 |
Validation Checklist
- Each consumer linked to a utility level / supply
- Steam levels chosen against grand composite curve
- CW ΔT fits site climate (10 °C temperate, 15 °C arctic)
- IA dryness ≤ −40 °C dew point in design basis
- Fuel-gas Wobbe variation within burner tolerance
- Utility load summary in
results.jsonunderutilitieswith duty + cost - CO₂ intensity calculated for project ESG metric
Related Skills
neqsim-heat-integration— pinch dictates utility levelsneqsim-power-generation— HRSG / steam networkneqsim-emissions-environmental— CO₂ from utility fuel