Compressor Deposit and Performance Degradation

This model links deposit-generating process calculations (elemental sulfur drop-out, salt from entrained produced water, mineral scale, wax, corrosion products) to centrifugal compressor performance. It answers three questions:

  1. How much deposit accumulates (from one or several mechanisms combined)?
  2. What is the effect on performance — polytropic efficiency, head, power, discharge temperature, and the degraded compressor chart after N operating hours?
  3. Where do the deposits form — which impeller / stage?

All deposit-to-performance relations are screening-level and the coefficients are exposed for calibration to measured (e.g. root-cause-analysis) degradation points.

Components

Class Purpose
DepositMechanism Deposit types (S8, NaCl, CaCO3/BaSO4/CaSO4, FeS, wax, …) each with a solid density
CompressorDeposit Mass-based, multi-mechanism deposit inventory → efficiency and head multipliers
DepositSource Interface: a precipitation calculation that yields a deposition rate
SolidFlashDepositSource Deposition rate from a TPSolidflash (S8, wax) on a stream
EntrainedSaltDepositSource Salt precipitation from evaporating entrained produced water
CompressorDepositProfile Per-impeller deposit location along the compression path
CompressorChart.getDegradedChart(...) Scaled (degraded) performance map
WashFluid Wash fluids (water, xylene, toluene, condensate, methanol) with deposit solubilities
CompressorDepositWash Recommend a wash fluid, plan the rate/duration, simulate the wash

1. Deposit mass to performance effect

CompressorDeposit converts an accumulated deposit mass to a fractional flow-area blockage and hence to a polytropic efficiency multiplier and a head multiplier:

\[V = \sum_i \frac{m_i}{\rho_i}, \quad t = \frac{V}{A_\text{wetted}}, \quad b = \min\!\left(\frac{t}{h_\text{passage}},\, b_\text{max}\right)\] \[m_\text{eff} = \max\!\left(1 - k_\text{eff}\, b,\ m_\text{eff,min}\right), \qquad m_\text{head} = \max\!\left((1-b)^{n_\text{head}},\ m_\text{head,min}\right)\]

where $m_i$ / $\rho_i$ are the deposit mass and density of each mechanism, $A_\text{wetted}$ is the foulable impeller area, $h_\text{passage}$ the flow-passage half-height, and the default coefficients are $k_\text{eff} = 1.6$ and $n_\text{head} = 2$.

// Size the foulable geometry from the compressor inlet flow, then add deposits.
CompressorDeposit dep = CompressorDeposit.fromCompressor(compressor);
dep.addDeposit(DepositMechanism.SULFUR_S8, 1.2);   // kg from a sulfur study
dep.addDeposit(DepositMechanism.SALT_NACL, 0.4);   // kg from a salt study

double effLoss  = 1.0 - dep.getEfficiencyMultiplier(); // fractional efficiency loss
double headLoss = 1.0 - dep.getHeadMultiplier();       // fractional head loss
double blockage = dep.getAreaBlockageFraction();

Calibrate to measured degradation:

dep.setEfficiencyBlockageCoefficient(1.6); // tune k_eff
dep.setHeadBlockageExponent(2.0);          // tune n_head
// Inverse: how much S8 deposit is consistent with a measured efficiency multiplier?
double kg = dep.depositMassForEfficiencyMultiplier(DepositMechanism.SULFUR_S8, 0.77);

Applying degradation to the simulation

Attaching the deposit model makes run() use the degraded machine — for a fixed outlet pressure the polytropic efficiency drops, so power and discharge temperature rise:

compressor.setPolytropicEfficiency(0.78);   // clean design efficiency
compressor.setDepositModel(dep);            // degradation now applied in run()
compressor.run();

double degradedEff = compressor.getPolytropicEfficiency(); // < 0.78
double power       = compressor.getPower();                // higher than clean
compressor.setDepositModel(null);           // restore clean machine

The degradation is applied from a fixed clean baseline, so repeated run() calls do not compound it.

2. Deposit amount from the process (precipitation bridge)

Instead of supplying the deposit mass by hand, compute it from the process thermodynamics. A DepositSource turns a precipitation calculation into a deposition rate, and CompressorDeposit.accumulate(source, hours) integrates it over an operating interval.

Elemental sulfur (and wax) — solid flash

// S8 carried in the (entrained-liquid-bearing) compressor feed drops out on flash.
SolidFlashDepositSource s8 =
    new SolidFlashDepositSource(feed, "S8", DepositMechanism.SULFUR_S8, 0.3); // 30% capture
double s8Rate = s8.getPrecipitationRate("kg/hr"); // thermodynamic drop-out rate
dep.accumulate(s8, 500.0);                          // deposit after 500 h

Salt from entrained produced water — mass balance

Salt (e.g. NaCl) is non-volatile, so it precipitates when entrained brine droplets dry out in the hot compressed gas:

EntrainedSaltDepositSource salt =
    new EntrainedSaltDepositSource(10.0, 0.05); // 10 kg/hr entrained water, 5 wt% salt
// Optionally estimate the evaporated water fraction from the actual duty:
double evap = EntrainedSaltDepositSource
    .estimateWaterEvaporatedFraction(feed, dischargeT_C, dischargeP_bara);
salt.setEvaporatedFraction(evap);
salt.setCaptureFraction(0.5);
dep.accumulate(salt, 500.0);

Model the entrainment upstream by mixing the carried-over liquid into the compressor feed (or via an imperfect separator efficiency); the flash then determines what precipitates.

3. Degraded chart after N operating hours

For a chart-based (fixed-speed) machine, degradation is applied through a degraded chart whose head and efficiency curves are scaled by the deposit multipliers:

compressor.setCompressorChart(cleanChart);
compressor.setDepositModel(dep);            // dep accumulated over 500 h

CompressorChart chart500 = compressor.buildDegradedChart(); // map after 500 h
double head500 = chart500.getPolytropicHead(flow, speed);       // reduced head
double eff500  = chart500.getPolytropicEfficiency(flow, speed); // reduced efficiency

CompressorChart.getDegradedChart(headMultiplier, efficiencyMultiplier) can also be called directly. When a chart is in use, the run-time efficiency multiplier is not additionally applied, so the efficiency loss is never double-counted.

4. Where the deposits form (per-impeller location)

Deposition happens where the local pressure and temperature cross the solubility limit. In a single compressor body the temperature rises from suction to discharge, so a solubility-limited species such as S8 concentrates on the cold first impeller and re-dissolves toward the hot last impeller; across a multi-stage train the gas re-cools in each intercooler and can re-deposit on the first impeller after each cooler.

Screening (interpolated stage pressure and temperature):

List<CompressorDepositProfile.StageDeposit> profile =
    CompressorDepositProfile.compute(feed, dischargeT_C, dischargeP_bara, 5, "S8");
int worst = CompressorDepositProfile.worstStage(profile); // usually 1 for a single body
for (CompressorDepositProfile.StageDeposit s : profile) {
  // s.getStage(), s.getPressureBara(), s.getTemperatureC(), s.getSolidRateKgHr()
}

Rigorous (uses the compressor’s real per-step flashed fluid states):

compressor.setPolytropicMethod("detailed");
compressor.getPropertyProfile().setActive(true);
compressor.run();
List<CompressorDepositProfile.StageDeposit> profile =
    CompressorDepositProfile.computeFromPropertyProfile(compressor, 5, "S8");

5. Live (online) washing — plan, recommend, and simulate

Washing removes deposit by dissolving it in a wash fluid. The WashFluid enum carries a screening solubility of each deposit mechanism, so a fluid only removes the deposits it can dissolve: water dissolves salt but not sulfur; xylene/toluene dissolve sulfur and wax but not salt; condensate dissolves wax. CompressorDepositWash uses this to recommend a fluid, plan the rate/duration, and simulate the wash.

\[\text{removed}_m = \min\!\big(\text{deposit}_m,\ \dot m_\text{fluid}\, S_m\, \eta_\text{contact}\, \Delta t\big)\]

where $S_m$ is the solubility (kg deposit / kg fluid) and $\eta_\text{contact}$ the contact efficiency (lower for online washing).

Recommend a wash fluid

WashFluid fluid = CompressorDepositWash.recommend(deposit);
// salt-dominated -> WATER; sulfur-dominated -> XYLENE/TOLUENE; wax -> CONDENSATE

Plan the wash

CompressorDepositWash washer = new CompressorDepositWash();
washer.setContactEfficiency(0.7);                        // online wash, imperfect contact

double rate = washer.requiredFluidRateKgHr(deposit, fluid, 4.0, 2.0); // 4 kg in 2 h
double hours = washer.hoursToRemoveMass(deposit, fluid, 200.0, 4.0);  // at 200 kg/hr
double dissRate = washer.dissolutionRateKgHr(deposit, fluid, 200.0);  // kg deposit/hr

Simulate the wash (updates the deposit model in place)

CompressorDepositWash.WashResult result = washer.wash(deposit, fluid, 200.0, 2.0);
result.getTotalRemovedKg();
result.getRemovedKg();                       // per mechanism
result.getEfficiencyMultiplierBefore();      // -> getEfficiencyMultiplierAfter()
result.getHeadMultiplierBefore();            // -> getHeadMultiplierAfter()
result.getRemainingDepositKg();

Online wash of a running compressor

compressor.setDepositModel(deposit);
WashFluid best = CompressorDepositWash.recommend(deposit);
CompressorDepositWash.WashResult r = compressor.washOnline(best, 300.0, 3.0);
compressor.run();   // power/discharge temperature recover toward clean

Recommending a wash strategy for mixed deposits

For mixed salt + sulfur fouling, a single fluid cannot remove everything — plan a sequence (e.g. water for the salt, then xylene for the sulfur). recommend returns the fluid that removes the most mass first; re-run it after each wash to plan the next step.

Scope and limitations