Guide · Layer 2

Close the Balance

Written for: seed / Series A scientist-founder

Don’t stop to perfect each box as you go. It’s usually faster to charge through end to end first — get a rough version of every unit connected and producing a number — then come back here to clean up, before the model gets too tangled to fix.

Closing the balance is that clean-up pass — it’s where the model’s mistakes tend to surface.

Close the balance

Make the streams reconcile — mass in = mass out — around each box and around the whole plant:

Check every component, not just the total — a balance can close overall while a single split is badly wrong
Watch the losses compound — shave 10–15% off at each of multiple steps and you can reach the product with a third of what you started with
A gap you can’t close is usually a missing stream — a vent, a purge, water of reaction. Hunt it down; don’t scale a stream to force closure
Kill the rounding — rounding a flow and then multiplying lops off real mass. It’s the first thing to check when a balance almost closes

🧭 Coach’s Read

Put your attention on the biggest streams — an error in a major feed moves equipment size and consumption both; a trace stream rarely changes the answer. When the algebra tangles, find a tie component — a species that rides straight through untouched backs out an unknown flow in one division. And lay the balance out inside each box (input → mechanism → output), not as one wide stream table; if you keep a stream table, make it display-only — every number calculated elsewhere and referenced in.

🪜 Leveling Up — rigorous thermo and kinetics

The step up replaces proxies with real phase equilibria, kinetic reactor models that predict conversion instead of assuming it, and formal pinch analysis for heat integration — usually inside the same process simulator Layer 1 flagged for solving loops. It’s worth doing when a P/T-sensitive equilibrium won’t yield to a proxy, when conversion is the thing you’re trying to predict, or when detailed design or a counterparty’s diligence demands it.

Once the flows and duties are fixed, the next layer puts dollars on them: Layer 3 — Economic Layer, where each duty becomes an equipment cost and each consumption figure becomes a cost per tonne.