Case study: plan, feasibility and ROI

Assumed case study: a milk pasteurisation and packaging section of a dairy plant (HTST process: raw milk tank, heat exchanger, steam-heated holding tube, cooling, filling). The existing system uses analog panel indicators, bimetal thermostats, a manual steam valve and operator logging. (If your own visit was to another plant, replace the process names; the structure of the answer stays the same.)

Existing system circumstances

 Raw milk tank --> pump --> heat exch. --> holding tube
   (level sw)      (motor    (steam valve    (72 C, 15 s)
                    starter)  manual)           |
                                        cooling --> filling
 Panel meters / thermostats  <-- operator reads, adjusts

Manual operation with analog gauges; no alarms and no records; operators control the steam valve by judgement.

Problem identification and analysis

Temperature varies by ±3 C (risk of under-pasteurised or burnt milk); about 1.5 percent of batches are rejected; steam is wasted; there are frequent power interruptions; there is no traceability; and the labour need is high. Cause analysis shows that the absence of feedback control and automatic logging is the root cause.

Recommendation plan

Install the microcontroller-based closed-loop control:

 PT100 --> Amp/SigCond --+
 Level sensor ----------+--> MUX/ADC (12-bit)
 Flow sensor ---(pulse)-+         |
 Keypad ----------------+---> [Microcontroller] <--> LCD 16x2
                               |  ARM/AVR + flash   |
   Opto + SSR/relay <----------+  watchdog, timers  +--> RS-485
     |                         |                          (Modbus)
 Pump / steam valve / alarm    +--> EEPROM log         PC / SCADA
 Power supply: 24 V + 5 V + UPS

Phases: (1) survey and design, (2) bench prototype and test, (3) pilot installation on one line in parallel with the old system, (4) full commissioning and training, (5) monitoring and review.

Requirement and feasibility analysis

• Technical: all components are available; the accuracy needed is ±0.5 C and the 12-bit ADC gives 0.037 C per count (calculated).
• Economic: investment Rs 12 lakh, monthly saving Rs 1.15 lakh, payback about 10.4 months (assumed).
• Operational: operators can be trained in two weeks; maintenance by plant technicians.
• Schedule: about 3 months.

Rollback plan

Keep the old manual valve and thermostat connected through a changeover switch. If the new controller fails in the pilot or later, switch back to manual control with little or no loss of production, and then debug the fault.

Advantages

• Technology: programmable, networked, upgradable.
• Production rate: less downtime and higher throughput.
• Quality assurance: consistent pasteurisation and records for audits.
• Cost-benefit and ROI: investment Rs 12,00,000 (controller panel, sensors, valves, SCADA PC, installation, training). Monthly savings: manpower Rs 60,000, steam/energy Rs 35,000, reduced rejection Rs 20,000 = Rs 1,15,000. Payback = 12,00,000 / 1,15,000 ≈ 10.4 months; yearly return = 13.8 lakh on 12 lakh, about 115 percent.