Concept
Capital expenditure (capex) is the one-time cost to design, build, and install a plant before it produces anything — the physical asset itself, as distinct from the recurring opex of running it. At the maturity anchor it’s built bottom-up from the major equipment: size each item, scale its cost, factor up to an installed total.
The factored build. Capex is estimated equipment-first, then grossed up:
The result is the inside-battery-limits (ISBL) cost — the process plant proper (see battery limits). Adding off-sites (OSBL) and indirects rolls it up to total capex, the figure that gets annualized. This page is the equipment build that feeds that roll-up.
Every figure carries its basis — currency, cost year (prices drift; escalate old figures), location, and battery-limits scope. Two figures add or compare only on the same basis; a borrowed reference cost (see reference / comparable process) must be converted first.
ISBL capex of a green-ammonia synthesis section, costing the few items that dominate: the syngas compression train and the ammonia reactor in the loop, the electrolyzer in the H₂ front end. The compression train — sized to 8 MW and scaled from a $2.0M / 5 MW reference with the six-tenths rule — comes in ~$2.7M purchased. Sum the loop’s big items, multiply by an installation factor (~3.5 for fluids) for installed ISBL, then add OSBL and indirects toward total capex.
Edge case: the shortcut weakens for the electrolyzer front end, where capacity is met by many identical stacks rather than one dominant vessel — no single big item to anchor the factor on, and cost lives in a module count instead (the numbering-up regime).