docs(scrubber): document GasScrubberMechanicalDesign + TR3500 conformity API

[dupuypablo]

Documents the full GasScrubber → GasScrubberMechanicalDesign → TR3500 conformity workflow and covers it with a runnable JUnit test.

Derived from the Kollsnes scrubber performance analysis task (task_solve/2026-04-20_kollsnes_scrubber_performance_analysis/), which runs 33 (scrubber × operating case) combos — 3 trains × 3 scrubbers × 11 cases including 2 historic peaks — through the documented API and produces a 9-table Sulzer-format performance deliverable (Excel + HTML).

Changes

• docs/process/equipment/separators.md — new section "Gas Scrubber Mechanical Design and Conformity Checking":

  • TR3500 rule set reference table (k-factor 0.15, inlet-momentum 15 000 Pa, mesh-k 0.27, drainage-head vessel-specific, cyclone-dp-to-drain 50 mbar)
  • Full Java workflow: initMechanicalDesign() → setInletNozzleID / setMeshPad / setDemistingCyclones / setInletDevice / setDrainPipeDiameterM / setLaHHElevationM / setLaHElevationM → setConformityRules("TR3500") → checkConformity() → iterate ConformityResult
  • Python equivalent
  • Multi-case screening pattern (design built once, fluid state updated per case)
  • Usage constraints (never modify TR3500 limits — subclass ConformityRuleSet instead; always initMechanicalDesign() before configuring internals; always process.run() between feed changes)

• src/test/java/neqsim/DocExamplesCompilationTest.java — new testGasScrubberConformityCheckDoc that exercises the full documented API and asserts a populated ConformityReport. Runs in ~2 s:

  Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 2.035 s
  

• docs/development/TASK_LOG.md — task entry summarising decisions (Tog1 historic point dropped due to missing PIC5063A; FAIL rates explained by swirldeck-fitted vessels being scored against the generic TR3500 mesh/k-factor rules).

Verification

• New doc test: ./mvnw test -Dtest=DocExamplesCompilationTest#testGasScrubberConformityCheckDoc — PASS
• Existing scrubber tests: ./mvnw test -Dtest='*Scrubber*' → KollsnesScrubberDesignTest 4/4 PASS, BUILD SUCCESS
• No source code changes — only docs + test.

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Note to reviewers: Please do not delete the scrubbers_kollsnes branch on merge — ongoing follow-up work will continue on it.

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Included fix: Hydrocyclone NPE (un-breaks Java 11 CI)

While reviewing CI on the sibling PR #2098 (which introduced the separator mechanical-design refactor), I found that every WaterTreatmentEquipmentTest test fails with NullPointerException at Separator.java:288 on both Java-11-Ubuntu and Java-11-Windows.

Root cause: Hydrocyclone.initMechanicalDesign() overrides the Separator method but only initializes hydrocycloneMechanicalDesign, leaving separatorMechanicalDesign null. The Separator(String) constructor calls initMechanicalDesign() and then immediately dereferences separatorMechanicalDesign on the next line → NPE.

Fix: one-liner — call super.initMechanicalDesign() first. Verified locally: WaterTreatmentEquipmentTest 35/35 PASS (was 8/35 with 27 NPEs).

[EvenSol]

Good update. This can be merged into master.