neqsim-utilities-specification

name	neqsim-utilities-specification
version	1.0.0
description	Utility system specification — steam levels (HP/MP/LP), cooling water (CW supply/return ΔT), instrument air dryness, fuel gas composition, nitrogen purity, demineralized water, refrigeration. USE WHEN: a task requires utility duty consolidation, utility-system sizing, ESG/energy reporting, or selecting between utility levels for a process service. Pairs with neqsim-heat-integration (grand composite curve drives utility level selection) and neqsim-power-generation (HRSG/steam network).
last_verified	2026-04-26

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.json under utilities with duty + cost
• CO₂ intensity calculated for project ESG metric

Related Skills

• neqsim-heat-integration — pinch dictates utility levels
• neqsim-power-generation — HRSG / steam network
• neqsim-emissions-environmental — CO₂ from utility fuel