Electrolyser stacks: sizing and the skid equipment inputs¶

The optional stacks: section of process/cells.yaml sizes electrolyser stacks of a cell of the same file for a product duty, and names the skid equipment a duty of process/duties.yaml sizes. cheme process stack evaluates each stack design: the cells and stacks, their electrical arrangement, DC power, output and envelope, and the reservoir, pump and tank inputs from the duty run at that arrangement. The results go into the files the existing tools already read (the equipment list's dimensions, the pumps' datasheet type_specific), so cheme layout build and cheme datasheets draft/fill take them from there. The code is chemeascode.domains.equipment.electrolyser_stack (model electrolyser-stack v1); the decision is ADR 0044. It builds on the cell, its measured performance and the duties.

The section¶

stacks:
  - id: STK-1
    title: CO2-to-CO stacks on a 48 V DC bus
    cell: BPM-100                    # a cell id of the cells: section
    tags: [E-101A, E-101B]           # equipment-list tags, one per stack
    product:
      component: CO                  # a product of the cell's reaction
      rate: {value: 0.1, unit: kg/h, provenance: given, source: "..."}   # or mol/s, kmol/h, t/d
      recovery: {value: 0.9, provenance: assumed, source: "..."}          # optional, default 1
      purity: {value: 0.95, provenance: given, source: "..."}            # declared, reported
      pressure: {value: 1.2, unit: bar(a), provenance: given, source: "..."}
    electrical:
      max_stack_voltage: {value: 48, unit: V, provenance: given, source: "the DC bus"}
      max_stack_current: {value: 100, unit: A, provenance: given, source: "..."}   # optional
      rectifier_efficiency: {value: 0.95, provenance: assumed, source: "..."}      # optional
      rectifier_max_current: {value: 500, unit: A, provenance: assumed, source: "..."}  # optional
    envelope:                        # per cell, ASSUMED until the vendor's drawing
      cell_pitch: {value: 8, unit: mm, provenance: assumed, source: "..."}
      end_plates: {value: 120, unit: mm, provenance: assumed, source: "..."}
      frame_margin: {value: 40, unit: mm, provenance: assumed, source: "..."}
    access:                          # clearances around each stack
      end: {value: 1.0, unit: m, provenance: assumed, source: "..."}
      side: {value: 0.8, unit: m, provenance: assumed, source: "..."}
    replacement:
      interval: {value: 8000, unit: h, provenance: assumed, source: "membrane life"}
      operating_hours: {value: 8000, unit: h/a, provenance: assumed, source: "..."}
    equipment:
      duty: SKID-150                 # a duty id of process/duties.yaml: its horizon is the campaign
      reservoir: {tag: T-101, margin: {value: 0.25, ...}, aspect_ratio: {value: 1.5, ...}}
      recirculation_pump:
        tag: P-101
        flow_per_area: {value: 0.5, unit: mL/(min cm2), provenance: assumed, source: "..."}
        density: {value: 1050, unit: kg/m3, ...}
        viscosity: {value: 1.2, unit: mPa s, ...}
        reservoir_pressure: {value: 101.3, unit: kPa, ...}
        stack_pressure_drop: {value: 50, unit: kPa, ...}
      dosing_pump: {tag: P-102, margin: {value: 0.5, ...}}
      dosing_tank:
        tag: T-102
        margin: {value: 0.2, ...}
        aspect_ratio: {value: 1.2, ...}
        refill_interval: {value: 168, unit: h, provenance: assumed, source: "..."}  # optional
      bleed_tank:
        tag: T-103
        margin: ...
        aspect_ratio: ...
        empty_interval: {value: 24, unit: h, provenance: assumed, source: "..."}    # optional

Every field is optional except id, cell, product and electrical.max_stack_voltage; the schema stays cheme/electrochemical-cells/v1. The stacks are not part of the cell's Faraday balance (cheme process cell reads none of it).

What is calculated¶

At the cell's operating point from cheme process cell (its current density j = I / A_cell, voltage U and Faradaic efficiency FE of the product; a measured cell's looked up at j in its series):

value	how
product formed	the duty over the `recovery` (default 1: formed = delivered): the share of the product formed that reaches the skid boundary (gas conditioning, purification), 0 < r <= 1
total active area	`A = n F Ndot / (nu FE j)` for the product formed `Ndot` (mol/s)
cells required	`ceil(A / A_cell)`
cells per stack	at most `floor(U_max / U)` in series; the stacks `ceil(cells / that)`; the cells shared evenly, `ceil(cells / stacks)` per stack
stack voltage, current	cells x `U`; the cell's current (one current through a series stack)
bus current, DC power	stacks x `I`; `P = sum N U I`; AC power over the rectifier efficiency; rectifiers for the rectifier current
output, margin	the integer arrangement's product formed and, with a recovery, delivered (never below the duty), and its margin over the duty
electricity, heat	kWh per kg of product formed (all the DC power) and, with a recovery, per kg delivered; the cell's heat per cell times the cells
envelope	`L = cells x pitch + end plates`, `W = H = sqrt(A_cell) + 2 x frame margin`; the footprint with the clearances
replacements	cells and membrane area replaced per year from the interval and the operating hours

From the duty named under equipment:, run at the sized arrangement (the cells per stack in series, the stacks on the one reservoir) over its horizon:

tag	gets	from
reservoir	list `dimensions` (diameter, height, `head: flat`, `support: none`)	the largest volume over the duty times one plus the margin, a vertical cylinder of the stated H/D
dosing tank	list `dimensions`	the solution dosed over the campaign, or with a `refill_interval` the most dosed in any window of min(campaign, interval), with the margin; the fills per campaign `ceil(campaign / interval)`
bleed tank	list `dimensions`	the bleed over the campaign, or with an `empty_interval` the most bled in any window of min(campaign, interval), with the margin; the emptyings per campaign
the duty's reservoir volume	`process/duties.yaml` `reservoir.volume`, when the duty states `reservoir.size: to_horizon`	the exact volume that reaches the duty's horizon (plus its time margin) at the pH threshold, `V0 Q(target) / Q*` (duties), written rounded up to 4 significant figures
recirculation pump	datasheet `type_specific`: `mass_flow_kg_h`, `density_kg_m3`, `viscosity_mpa_s`, `suction_pressure_kpa`, `discharge_pressure_kpa`, `suction_from`, `discharge_to`	the anolyte flow per area (or per cell) times the cells at the density; the reservoir pressure and the stack's pressure drop; the reservoir's tag and the first stack's tag (the stacks in parallel share the inlet header)
dosing pump	datasheet `mass_flow_kg_h`, `density_kg_m3`	the duty's dosing rate times one plus the margin (its end points and pressures are declared by hand)
stack tags	list `dimensions` (length, width, height)	the envelope

The window of an interval is exact on the duty's transient: the dosing and bleed rates are constant between its samples (the dosing switches are sampled), so the largest increase of the dosed or bled total over a window starts or ends at a sample. Without an interval a tank holds the campaign's total, as before.

Every value carries its provenance (given, assumed, calculated, or tbd with the reason) and its source; a value resting on an assumed input is marked ASSUMED. A tank is a flat-ended cylinder over its whole height: a list that states another head or a support for it (which the 3D model puts inside that height, so the shell would hold less) keeps its sizes (cheme.stack-kept).

One design basis¶

The cell's operating point, the arrangement and the duty are stated once:

the stack is sized at the cell's current density in the cells: section. A duty that runs the cell at another current density, or runs another cell, gives no reservoir, dosing or bleed inputs (cheme.stack-duty, error): the duty states the stack's operating point, or the stack is sized at the duty's;
the arrangement comes from the sizing. cheme process stack runs the duty at it, and cheme process duty runs a duty a stack names at the same arrangement (cheme.duty-arrangement, info), so the two commands give one result for one duty id. A duty's own cells_in_series and stacks are then not used (cheme.stack-duty, info: drop them). One duty runs at one arrangement: the first stack naming it has it, and a later stack naming the same duty gets no reservoir, dosing or bleed inputs (cheme.stack-duty, error);
a duty that is no stack's skid duty, such as a comparison duty on the skid's hardware, names the stack itself (stack: STK-1 in process/duties.yaml): cheme process duty and --compare run it at that stack's arrangement too. Such a duty stating cells_in_series or stacks other than the stack's, naming a stack that is not in the file or is of another cell, or being another stack's skid duty, is refused (cheme.duty-arrangement, error); the stack's own skid inputs still come from its equipment.duty only. A skid duty that names its own stack and states another cells_in_series or stacks is refused by both commands (cheme.stack-duty and cheme.duty-arrangement, errors: no tank or dosing inputs);
one item, one size: a tag two stacks (or two roles of one skid) name is written by neither (cheme.stack-tags, error).

Where the results go¶

Without --write, cheme process stack writes nothing and reports each target that differs from the file (cheme.stack-outdated). --write edits the equipment list in place (comments and the rest of the file kept; the edit must change only the named dimensions, or nothing is written) and the pumps' datasheets, and only a value that is missing, TBD or written by cheme process stack before. A value written by hand is kept and reported (cheme.stack-kept). A value cheme process stack wrote that the design basis no longer gives (an envelope or a pump input removed, a duty no longer feasible) is reported outdated too; --write sets a datasheet value TBD with the reason and removes the list sizes (sizes beside a weight are kept: cheme.stack-kept, clear them by hand). A duty with reservoir.size: to_horizon asks for its reservoir volume: --write writes it into process/duties.yaml (in place, comments kept, only that volume changed, with its source), and in the same run the tanks from the duty at that volume (before it, the duty at the stated volume is not feasible and gives no tank sizes). With --json, the report (as the files are after the write) carries written: each file written with its tags (or duty ids).

The equipment list's dimensions take three optional fields for sizes a tool calculated:

field	meaning
`source`	where the sizes come from (`cheme process stack: stack STK-1, duty SKID-150 at ...`); a source starting with `cheme process stack` marks them as the tool's, to rewrite
`assumed`	the sizes rest on an assumption (marked ASSUMED)
`fingerprint`	of the inputs the sizes were calculated from; `cheme process stack` compares it to report a stale size

cheme datasheets draft and fill carry source and assumed onto the datasheet's main dimensions (derived_dimensions); the fingerprint stays in the list. Then rerun:

cheme layout build: the 3D model's body of each tag from its list dimensions;
cheme datasheets draft / cheme datasheets fill --tag TAG: the tanks' volume, and the recirculation pump as a pump no flowsheet stream links: its flow from the mass flow and density, its head, NPSH and power along the routed lines from suction_from (the reservoir) to discharge_to (the stack). Those lines come from the skid's P&ID routed in the layout model; until they exist the head, NPSH and power stay TBD with that reason. The dosing pump gets its capacity only: declare its end points and pressures by hand.
cheme assess lca: it reads the flowsheet's energy and material streams, not the stacks. Enter the stacks' DC power (or the AC power, with the rectifier inside the boundary) as the duty of the electricity stream into the electrolysis step (the stream a cell's flowsheet.electricity names) and the dosing as the stream into the reservoir. Nothing reports those stale when the stacks change: compare them after each change.

The skill skid-design chains the whole sequence.

Checks and refusals¶

rule	level	when
`cheme.stack-schema`	error	a unit a quantity does not take, a duplicate stack id, a value out of its range (not above 0: product rate, voltage and current limits, rectifier current, cell pitch, replacement interval, H/D, anolyte flow, density, viscosity, reservoir pressure, a refill or emptying interval; a recovery not in (0, 1], which refuses the stack; below 0: end plates, frame margin, clearances, operating hours, a margin, the stack's pressure drop; a rectifier efficiency not in (0, 1]): the value is not used (a stated voltage or current limit refuses the stack; a rectifier efficiency leaves only the AC power out)
`cheme.stack-cell`	error	the cell is missing, refused by its Faraday balance (outside the measured range among others), has no active area, does not form the product, a side reaction forms or consumes the product too (the Faradaic efficiency is the overall reaction's: name the main product), or a specified cell is outside its declared operating range: the stack is refused, never extrapolated
`cheme.stack-electrical`	error	the cell voltage above the stack voltage limit, or the cell current above the stack current limit
`cheme.stack-duty`	error / info	the duty is missing, runs another cell or another current density, is refused or not feasible at the sized arrangement, names another stack (`stack:`), names this stack and states another `cells_in_series` or `stacks`, or an earlier stack names it (no tank and dosing inputs); info: the duty states another arrangement
`cheme.stack-envelope`, `stack-input-missing`	info	an envelope or equipment input is missing: that value stays TBD
`cheme.stack-unsourced`	info	an assumed input without a source
`cheme.stack-tags`	warning / error	fewer or more tags than stacks, or a tag not in the equipment list; error: a tag given twice (two stacks, or two roles), written by neither
`cheme.stack-outdated`	warning	a list dimension, datasheet input or a duty's reservoir volume (`size: to_horizon`) differs from the calculated one, or one `cheme process stack` wrote is no longer given: `--write`
`cheme.stack-kept`	warning	a value written by hand differs: kept; a tank stating a head or a support; sizes no longer given beside a weight
`cheme.stack-target`	info	the item or datasheet a value goes to does not exist

cheme validate reports the findings that need no duty run (the sizing, the cell, the tags and the stacks' list dimensions). A process/cells.yaml that does not follow its schema makes cheme process stack print its cheme.cell-schema findings and exit 1.

Limitations¶

The stack voltage counts the cells only (no busbar, contact or cable losses); the rectifier is an efficiency and a current rating, not a design. Stacks are in parallel on one bus; series strings of stacks are not sized.
The envelope is a square active area with an assumed pitch and margins, not a vendor's drawing; a tank is its working volume's cylinder (flat ends, no support, wall not added).
The anolyte flow per area or per cell is declared (the measured series states none); the pump head is the stack's declared pressure drop plus the routed lines of the pump sizing.
No hazardous area, gas handling (H2, CO) or venting is sized.
The LCA does not read the stacks: their power and the dosing go into the flowsheet streams by hand, and nothing reports those stale.
cheme validate does not yet check the duty-dependent list sizes (tanks) for staleness; rerun cheme process stack after a duty change.