Equipment functions, utilities and process integration

Equipment performs a specified change

A pump supplies mechanical energy to a liquid stream; a compressor performs a pressure-raising function for a gas. Heat-exchange equipment transfers energy between streams, while a separator changes how material is distributed among outlets. A reactor provides conditions for chemical change. These functions can interact, so distinguish a unit’s intended role from every effect it has on the process.

A functional box does not establish a suitable equipment type, material, capacity or operating range. The process record must connect inlet and outlet conditions, required performance and constraints to further equipment analysis. For example, a separation target can change subsequent heat demand, and a pressure change can alter phase conditions. A consistent flowsheet keeps those dependencies visible.

Recoverable heat is an internal transfer

Suppose an original recipient stream requires 100 kW. Assume that 60 kW can feasibly transfer from another process stream at compatible temperatures and times. The remaining external hot-utility demand is 40 kW under the stated steady assumptions. A utility is a supporting energy or material service, such as heating, cooling or electrical power; its source and boundary still matter.

Across a boundary containing both process streams, their internal 60 kW transfer cancels: it leaves one included stream and enters the other. Do not count it as new energy created by integration or as two independent savings. The source’s cooling requirement and the recipient’s heating requirement change together; the overall account must include both.

Quantity alone does not establish recoverability

A hot stream’s available energy does not mean it can meet any colder stream’s entire demand. Temperature differences and profiles constrain transfer, and finite transfer coefficients and surface area affect achievable duty. Timing matters if one stream is intermittent. Material compatibility, fouling, pressure containment and contamination constraints can make a seemingly attractive connection unsuitable.

Integration also couples operation. Starting one unit may require a utility before a second stream becomes available; disturbances can propagate through shared heat exchange. Consider controllability, isolation for maintenance and the service required during changing conditions. A reduction in one steady utility account does not automatically establish lower total cost, lower life-cycle impact or adequate operation across the intended range.

A stronger source can supply less useful heat

Add time to the original recipient account. In this separate constructed case the recipient needs 100 kW continuously for two hours. The required service is therefore 100×2=200 kWh. Compare source S, which can supply 60 kW during the first hour only, with source T, which can supply 40 kW during both hours. Assume transfer at those rates is feasible at compatible temperatures while each source is available. There is no heat storage or heat pump, and external utility must supply the remaining demand at each instant.

With S, utility is 100−60=40 kW in hour one, but 100 kW in hour two. Its energy is 40×1+100×1=140 kWh. With T, utility is 60 kW throughout, giving 60×2=120 kWh. The smaller recovery rate supplies 80 kWh in total instead of 60. Comparing only the largest available kW number would choose the wrong source for reducing utility energy in this service window.

Now stipulate utility equipment able to deliver at most 80 kW. S leaves a 20 kW shortfall in the second hour: balancing 200 kWh over a period cannot move first-hour heat to that later hour without a storage process. T stays below the cap at 60 kW and meets the supplied time-by-time account. This is a conditional comparison, not evidence that an exchanger or utility actually meets those duties. The source/sink temperatures, transfer capability and actual schedules still need corresponding observations.

Distinguish a balance from a feasible design

The recipient account is 60+40=100 kW. If a compatible internal source could supply only 45 kW instead, external hot utility would become 55 kW under unchanged assumptions. This arithmetic is an account conditional on achievable transfer, not a method for deciding that the proposed exchanger can deliver either figure.

To compare the alternatives, retain the recipient target, source and sink temperature profiles, timing assumptions and evidence behind the estimated internal duty. Then compare additional equipment, utility consumption, maintenance, control and life-cycle effects on an equal-service basis. The simplified bar diagram encodes the supplied duty split; it does not present equipment dimensions or an optimum network.

For the added schedule comparison, check both energy closure and peak power. S gives 60+140=200 kWh over the window but fails the 80 kW utility cap during hour two. T gives 80+120=200 kWh and needs only 60 kW utility. A missing source interval is a physical dependency, not a discrepancy that can be repaired by averaging the two hourly powers.

Try the reasoning

1. Why does internal heat transfer cancel across a boundary containing both streams?

   Show the answer and reasoning

   The same energy leaves one included stream and enters another, so it is not an external input to the combined system.

2. If only 45 kW of the 100 kW demand is recoverable, what utility remains?

   Show the answer and reasoning

   55 kW, assuming the required duty and all other conditions stay unchanged.

3. Does an available heat quantity prove that a proposed transfer is achievable?

   Show the answer and reasoning

   No. Temperature profiles, transfer capability, timing and equipment constraints also need evidence.

4. Suppose T is available for only the first 1.5 h, with all other assumptions unchanged. Compare its utility energy with S and decide whether an 80 kW utility can serve the whole window.

   Show the answer and reasoning

   T supplies 40×1.5=60 kWh. Utility is 60 kW for 1.5 h and 100 kW for 0.5 h, totalling 90+50=140 kWh: equal to S’s energy. Both nevertheless fail the 80 kW utility cap when their recovery source is unavailable. Equal total energy does not establish the same schedule or time-by-time feasibility; another supported source, storage or changed service would require a new account.

What to carry forward

Connect equipment functions and internal transfers to a complete account, then establish feasibility and operating consequences separately.