Slide 1 — Title: IRP Sensors

This lecture is about sensors used in process instrumentation and regulation. In process engineering, sensors are the “eyes and ears” of a system 👀. They measure physical or chemical variables so that a process can be monitored, controlled, optimized, and made safe.

The lecture focuses on typical sensors used in chemical/bioprocess systems, such as sensors for flow, temperature, pressure, liquid level, mass, and pH.

Slide 2 — Content overview

The main topics are:

1. Mass
2. Temperature
3. Pressure
4. Flow
5. pH

These are core process variables. In a fermentation or chemical plant, you often need to know:

• how much material is present,
• how fast it is moving,
• how hot it is,
• how much pressure exists,
• and whether the liquid is acidic or basic.

These measurements are essential for both process safety and product quality.

Slide 3 — What do we want from sensors?

This slide introduces important sensor-performance concepts:

Limit of Detection, LOD

The limit of detection is the smallest signal or concentration that can be reliably detected above background noise.

The slide gives:

LOD = 3 × standard deviation

That means the measured signal must be at least three times higher than the noise variation to be considered detectable.

Limit of Quantification, LOQ

The limit of quantification is the smallest amount that can be measured accurately enough to give a reliable number.

The slide gives:

LOQ = 10 × standard deviation

So LOQ is stricter than LOD.

Simple explanation 🧠

Imagine trying to hear a whisper in a noisy room.

• LOD: You can tell someone is whispering.
• LOQ: You can clearly understand what they are saying.

For sensors, this matters because a sensor may detect that something is present, but not measure exactly how much is present.

Slide 4 — Venturi flow meters

A Venturi flow meter measures flow using a narrowed section of pipe.

Principle

It is based on Bernoulli’s principle.

When fluid passes through a narrow section:

• velocity increases,
• pressure decreases.

By measuring the pressure difference before and inside the narrow section, the flow rate can be estimated.

Important equation

Q = A × v

Where:

• Q = volumetric flow rate,
• A = cross-sectional area,
• v = fluid velocity.

Advantages

Venturi meters are mechanically simple and can measure flow without moving parts.

Downsides

The slide highlights two important disadvantages:

1. Pressure loss
   • The fluid loses some pressure when passing through the constriction.
2. Density must be known
   • Flow calculations depend on fluid density.
   • Density depends on temperature and liquid composition.

So Venturi meters work best when the liquid properties are known and fairly constant.

Slide 5 — Vortex flow sensor from Grundfos

This is mostly an image slide showing a commercial vortex flow sensor.

What the image is showing

A vortex sensor contains an obstruction inside the flow path, called a bluff body. When fluid flows around this object, vortices are shed alternately from each side.

This creates a repeating pattern of swirls, known as a vortex street 🌪️.

The sensor detects the frequency of these vortices. Since vortex frequency is related to flow velocity, the sensor can calculate flow rate.

Why this is useful

Vortex sensors are useful because they convert a physical fluid phenomenon into a measurable signal.

In simple terms:

Faster flow → more vortices per second → higher measured frequency.

Slide 6 — Vortex flow

This slide explains vortex flow in more detail.

Strouhal number

The slide gives the Strouhal relationship:

St = f × d / v

Where:

• St = Strouhal number,
• f = vortex frequency,
• d = width of the bluff body,
• v = flow speed.

The slide states:

St = 0.18 for Re = 300–10⁷

That means over a large Reynolds number range, the relationship between vortex frequency and flow velocity is predictable.

Limitations

The slide lists several practical limitations:

• limited measuring range,
• no particles,
• depends on liquid and temperature,
• no air bubbles in the liquid,
• pressure loss through the sensor.

Interpretation

Vortex meters are useful for clean, single-phase liquids. But they are not ideal for dirty suspensions, foamy liquids, or bubbly liquids.

For example, if you have yeast cells or gas bubbles in the liquid, they may disturb vortex formation and make the measurement unreliable.

Slide 7 — Electromagnetic flowmeter

An electromagnetic flowmeter measures flow using Faraday’s law of electromagnetic induction.

Principle

When an electrically conductive liquid moves through a magnetic field, a voltage is induced.

The induced voltage is proportional to the velocity of the liquid.

So:

Moving conductive liquid + magnetic field = measurable voltage ⚡

Advantages

The slide says electromagnetic flowmeters are:

• independent of viscosity,
• able to handle liquids with particles,
• useful for electrically conductive liquids.

This is very useful in bioprocessing, where liquids may contain cells or suspended particles.

Limitations

The liquid must be electrically conductive.

Also, the slide notes:

• no air in the liquid.

Air bubbles can disturb the signal because air is not conductive and changes the effective measurement.

Important example

A suspension of yeast cells in water could be suitable for an electromagnetic flowmeter, because the liquid phase is conductive and the particles can be tolerated.

Demineralized water, however, is problematic because it has very low conductivity.

Slide 8 — Ultrasonic flowmeter

An ultrasonic flowmeter uses sound waves to measure flow.

Principle

Sound waves are sent through or along the liquid. The flow affects how long the sound takes to travel.

If the liquid flows in the same direction as the sound, the sound arrives faster. Against the flow, it arrives slower.

The difference can be used to calculate flow velocity.

Advantages

The slide says ultrasonic flowmeters are good for:

• high flows,
• large pipes.

They can often be installed without major pipe modifications, depending on type.

Limitations

The slide notes that they depend on:

• temperature,
• liquid type,

because the speed of sound changes depending on the medium and temperature.

Particles and bubbles disturb measurements. This is because bubbles and solids scatter or absorb ultrasound.

Practical meaning

Ultrasonic flowmeters are good for clean liquids in large systems, but less reliable for aerated fermentation broth or particle-rich suspensions.

Slide 9 — Mass flowmeters

This slide describes mass flowmeters, especially Coriolis-type mass flowmeters.

Principle

The slide says they detect a “twist” when a liquid is circulated in a loop.

In a Coriolis flowmeter, tubes vibrate while fluid flows through them. The moving mass creates a twisting effect due to Coriolis forces.

The stronger the twist, the higher the mass flow.

Why this is powerful

Unlike many other flowmeters, mass flowmeters measure mass flow directly, not just volume flow.

That means they are especially useful when density changes.

Advantages

The slide says:

• suitable for all types of flows,
• most precise flowmeter.

Disadvantage

They are expensive 💸.

When to use

A mass flowmeter is often a good choice when liquid composition or temperature changes, because it directly measures mass flow and is less dependent on density assumptions.

Slide 10 — Which flowmeter would you use?

This is a discussion slide asking you to choose flowmeters for different cases.

Case 1: Suspension of yeast cells in water

Best choice: electromagnetic flowmeter.

Why?

• yeast cells are particles,
• electromagnetic flowmeters can handle particles,
• water-based broth is usually conductive.

Avoid vortex and ultrasonic if the suspension or bubbles disturb measurement.

Case 2: Demineralized water

Best choice: likely ultrasonic or possibly mass flowmeter.

Why not electromagnetic?

• demineralized water has low conductivity,
• electromagnetic flowmeters require conductive liquid.

A Venturi meter could also work if density is known, but it causes pressure loss.

Case 3: Liquid of varying composition and temperature

Best choice: mass flowmeter.

Why?

• varying composition changes density,
• varying temperature also affects density and sound speed,
• mass flowmeters directly measure mass flow and are highly precise.

Slide 11 — Resistive temperature sensors, RTD

This image-heavy slide introduces RTDs, or resistance temperature detectors.

Principle

An RTD measures temperature through a change in electrical resistance.

For metals such as platinum:

Higher temperature → higher resistance

The relationship is approximately linear over many temperature ranges.

Temperature coefficient

The slide defines a temperature coefficient, α, with unit:

K⁻¹

This coefficient describes how much the resistance changes per degree of temperature change.

Simple explanation 🌡️

An RTD is like a thermometer where the “reading” is not mercury height, but electrical resistance.

If resistance increases in a predictable way, you can convert resistance into temperature.

Slide 12 — Platinum thermometer

This slide focuses on platinum RTDs.

Why platinum?

Platinum is commonly used because it has:

• stable resistance behavior,
• good accuracy,
• good chemical resistance,
• predictable temperature dependence.

Temperature ranges

The slide distinguishes between:

• −200°C to 0°C
• 0°C to 850°C

Different equations are used in different ranges because the resistance-temperature relationship is not perfectly linear across all temperatures.

Pt100, Pt500, Pt1000

The standard EN 60751 defines common platinum sensors:

• Pt100: R₀ = 100 Ω at 0°C
• Pt500: R₀ = 500 Ω at 0°C
• Pt1000: R₀ = 1000 Ω at 0°C

Example

For a Pt100:

• at 0°C, resistance is 100 Ω,
• at 20°C, resistance is about 108 Ω.

So a small resistance change corresponds to a temperature change.

Slide 13 — 2-point method is problematic

This slide explains a measurement problem with RTDs.

What is the 2-point method?

In a 2-wire setup, the same two wires are used to:

• send current through the RTD,
• measure voltage across it.

The problem is that the wires themselves have resistance.

Wire resistance

The slide gives:

• Rl = wire resistance,
• for 1 m copper wire with diameter 2 mm, resistance is about 5 mΩ,
• Pt100 resistance at 20°C is about 108 Ω.

Why this matters

The measured resistance becomes:

RTD resistance + wire resistance

Even if wire resistance is small, it can introduce error, especially when measuring very precisely.

Simple analogy

It is like trying to measure the weight of flour while forgetting that the bowl also has weight. The bowl may be small compared with the flour, but for precise measurements it matters.

Slide 14 — Solution: 4-point method

The 4-point method solves the wire-resistance problem.

How it works

Four wires are used:

• two wires carry current,
• two separate wires measure voltage.

Because the voltage-measuring instrument has very high internal resistance, almost no current flows through the sensing wires.

The slide states:

Ri >> Rl + R

This means the internal resistance of the measuring instrument is much larger than the wire resistance and sensor resistance.

Why this helps

Since almost no current flows through the voltage-sensing wires, there is almost no voltage drop across those wires.

So the measured voltage is much closer to the true voltage across the RTD.

Practical meaning

The 4-point method gives a much more accurate temperature measurement, especially for precision sensors like Pt100.

Slide 15 — Wheatstone bridge

This slide shows that a Wheatstone bridge can be even better for measuring small resistance changes.

What is a Wheatstone bridge?

It is an electrical circuit used to detect small resistance differences.

The RTD is placed as one resistor in the bridge. As temperature changes, the RTD resistance changes, and this creates a measurable output voltage.

Slide example

The slide gives:

At 10°C:

• RPt100 = 104 Ω
• Vout = 8 mV

At 20°C:

• RPt100 = 108 Ω
• Vout = 16 mV

So a small resistance change becomes a measurable voltage change.

Why it is useful

The Wheatstone bridge makes small changes easier to detect and can reduce the effect of unwanted noise or wire resistance.

Important note

The slide compares ratios and shows that output voltage can scale with resistance change. That makes the bridge useful for converting sensor resistance into an electrical signal.

Slide 16 — Thermocouples

Thermocouples are another type of temperature sensor.

Principle

A thermocouple consists of two different metals joined at a junction.

When the junction is heated, electrons move from the warm region toward the cold region.

This produces a voltage difference.

This is called the Seebeck effect.

Key point

The voltage depends on the temperature difference between the hot junction and a reference junction.

Therefore, the slide says:

You need a reference to find an absolute temperature.

Advantages

Thermocouples are:

• small,
• cheap,
• fast,
• good for high temperatures.

Limitation

They are generally less precise than RTDs and require reference-temperature compensation.

Slide 17 — Comparison: Thermocouples vs RTD

This slide compares the two temperature sensor types.

Thermocouples

Thermocouples are:

• smaller,
• usually use 2 wires,
• respond quickly,
• do not suffer much from self-heating,
• require a reference temperature,
• may drift over time,
• less precise.

The slide lists thermocouple precision around 0.1 K.

RTDs

RTDs are:

• bigger,
• can use 2 or 4 wires,
• slower,
• may have self-heating,
• do not require a reference temperature,
• drift less,
• more precise.

The slide lists RTD precision around 0.01 K.

Simple choice rule

Use a thermocouple when you need fast, robust, high-temperature measurement.

Use an RTD when you need high precision and stability.

Slide 18 — Pressure

This slide introduces pressure.

Definition

Pressure is force divided by area:

Pressure = Force / Area

Unit:

Pa = N/m²

Simple explanation

Pressure tells you how much force is applied over a surface.

For example:

• the same force over a small area gives high pressure,
• the same force over a large area gives lower pressure.

Why pressure matters

In process systems, pressure affects:

• flow,
• boiling point,
• membrane filtration,
• safety,
• pump requirements,
• tank and pipe design.

Pressure sensors are therefore very important in industrial systems.

Slide 19 — Strain gauge: pressure and mass

This image-heavy slide introduces strain gauges.

Principle

A strain gauge measures deformation.

When a material bends, stretches, or compresses, the strain gauge attached to it also deforms. This changes its electrical resistance.

For pressure

Pressure can bend a diaphragm. A strain gauge attached to the diaphragm detects the bending.

For mass

Mass creates force due to gravity. That force can deform a beam or load cell. The strain gauge detects the deformation.

Simple idea 🏋️

Strain gauges convert mechanical deformation into an electrical signal.

More force or pressure → more deformation → larger resistance change.

Slide 20 — Strain gauge with Wheatstone bridge

This slide explains that strain gauges are often used in a Wheatstone bridge.

Why?

The resistance changes in a strain gauge are very small.

A Wheatstone bridge makes these tiny changes easier to measure.

Temperature compensation

The slide says the Wheatstone bridge gives:

• more precise measurement,
• no influence of temperature.

More accurately, the bridge can reduce or compensate for temperature effects, especially when several strain gauges are arranged so temperature affects them similarly.

Practical meaning

This is useful in pressure sensors and weighing systems, where high precision is needed.

Slide 21 — Piezoresistive pressure sensor

A piezoresistive pressure sensor uses the piezoresistive effect.

Principle

When mechanical stress is applied to certain materials, their electrical resistance changes.

This is similar to a strain gauge, but often implemented directly in silicon microstructures.

How it works

Pressure deflects a thin membrane. Piezoresistors on the membrane experience stress, causing their resistance to change.

The sensor electronics convert this resistance change into a pressure reading.

Why useful?

Piezoresistive sensors are common because they can be:

• small,
• sensitive,
• integrated into electronic devices,
• suitable for pressure transducers.

Slide 22 — Measuring pressure

This slide shows different ways of measuring pressure.

Main pressure types

Absolute pressure

Measured relative to vacuum.

Example:

• atmospheric pressure is about 1 bar absolute.

Gauge pressure

Measured relative to atmospheric pressure.

Example:

• a tire pressure gauge shows pressure above atmospheric pressure.

Differential pressure

Measured as the difference between two pressures.

Example:

• pressure drop across a filter,
• liquid level from hydrostatic pressure,
• pressure drop across a flowmeter.

Why this matters

You must know what reference your pressure sensor uses. Otherwise, a pressure value can be misunderstood.

Slide 23 — Level sensing by differential pressure

This slide explains liquid level measurement using pressure.

Principle

The pressure at the bottom of a tank depends on the liquid height.

The relationship is:

ΔP = ρgh

Where:

• ΔP = pressure difference,
• ρ = liquid density,
• g = gravitational acceleration,
• h = liquid height.

Meaning

If you know the density of the liquid, you can calculate the liquid level from the pressure.

Limitations

The slide notes:

• depends on liquid density,
• sensitive to sediment and dirt.

If density changes, the level estimate becomes wrong. If sediment blocks the pressure connection, the measurement can fail.

Slide 24 — Pneumatic level measurement

This slide shows pneumatic level measurement, also called a bubbler system.

Principle

Gas is bubbled through a tube into the liquid. The pressure needed to push bubbles out equals the hydrostatic pressure at the tube opening.

That pressure tells you the liquid level.

Advantages

The slide says it is good for:

• dirty liquids,
• flammable liquids,
• digesters.

Why?

The sensor itself does not need to be in direct contact with the dirty or aggressive liquid. Only the tube contacts the liquid.

Practical example

In a biogas digester or wastewater tank, direct sensors may get dirty or clogged. A pneumatic system can be more robust.

Slide 25 — Ultrasonic level gauging

Ultrasonic level sensors measure distance using sound.

Principle

The sensor sends an ultrasonic pulse downward. The pulse reflects from the liquid or solid surface and returns to the sensor.

The time delay gives the distance to the surface.

Advantages

The slide says ultrasonic level gauging works for:

• liquids,
• solids.

It is also independent of liquid density.

Limitations

The slide notes it is limited by:

• foam,
• dust,
• dirt on the sensor.

Foam and dust scatter the sound waves and make the echo hard to interpret.

Practical meaning

Ultrasonic level sensors are useful when you want non-contact measurement, but they need a clear acoustic path.

Slide 26 — Level switch

This slide introduces level switches.

What is a level switch?

A level switch does not continuously measure the exact level. Instead, it detects whether the level is above or below a certain point.

Example functions

A level switch can tell you:

• tank is full,
• tank is empty,
• level has reached a safety limit,
• pump should turn on or off.

Difference from level sensor

A level sensor gives a continuous value.

A level switch gives a binary signal:

• yes/no,
• on/off,
• high/low.

Practical use

Level switches are often used for safety and automation, for example preventing overflow or dry-running of pumps.

Slide 27 — pH sensors

This slide introduces pH measurement.

What is pH?

pH measures hydrogen ion activity.

Low pH means acidic. High pH means basic.

pH-sensitive glass

The slide shows a reaction involving hydrogen ions and the glass surface:

H⁺ / −O−Si− ⇔ H⁺ + −O−Si−

This represents how hydrogen ions interact with silanol groups on the glass surface.

Principle

A pH electrode has a special glass membrane that develops an electrical potential depending on H⁺ activity.

The voltage difference is related to pH by the Nernst equation.

Simple explanation 🍋

The glass membrane behaves differently depending on how many hydrogen ions are in the solution. This creates a voltage, and the instrument converts that voltage into pH.

Slide 28 — pH electrode

This slide shows the structure of a pH electrode.

Main components

The slide labels:

• pH-sensitive glass,
• internal electrode, often Ag/AgCl,
• internal KCl solution,
• reference electrode,
• reference internal KCl solution,
• porous junction,
• non-conductive glass casing.

Why reference electrode is needed

The pH-sensitive glass gives a potential depending on pH, but to measure voltage you need a reference potential.

So a pH electrode is really an electrochemical cell.

Practical limitations

The slide says pH electrodes are:

• vulnerable,
• require maintenance,
• need electrolyte care,
• need recalibration,
• require temperature compensation.

Why temperature compensation matters

pH electrode response depends on temperature. Without compensation, the same voltage could correspond to slightly different pH values at different temperatures.

Slide 29 — Recap: Batch fermentation

This slide shifts from sensors to a fermentation process case.

What is batch fermentation?

In batch fermentation, substrate and microorganisms are added to a reactor, and the process runs for a defined time without continuous product removal.

After fermentation, the batch is harvested.

What the diagram likely shows

The P&ID-style diagram likely includes:

• fermenter vessel,
• feed or substrate addition,
• temperature control,
• agitation,
• sensors,
• outlet/harvest line,
• possibly gas handling.

Relevant sensors

For a batch fermenter, typical sensors include:

• temperature sensor,
• pH sensor,
• pressure sensor,
• level sensor,
• flow sensors on feed or cooling lines,
• possibly dissolved oxygen sensor,
• mass or load cells.

Process meaning

Batch systems are simpler than continuous membrane systems but require larger reactor volume for the same average production capacity.

Slide 30 — Recap: Continuous fermentation with MF

MF means microfiltration.

What continuous fermentation with MF means

In continuous fermentation, fresh substrate enters continuously and product-containing liquid leaves continuously.

The membrane retains microorganisms while allowing product and byproducts to pass through.

Why use membrane filtration?

The membrane keeps cells inside the reactor. This allows higher cell concentration and potentially smaller reactor size.

Cost comparison focus

The slide says the comparison focuses only on parts that are different:

CAPEX

Capital expenditure:

• reactor size,
• pumps.

OPEX

Operating expenditure:

• membrane replacement,
• pump electricity,
• maintenance.

Meaning

The comparison does not include every possible cost, only the costs that differ between alternatives. This is a useful simplification for a mini project.

Slide 31 — Dimension of reactors

This slide compares reactor dimensions for equal ethanol production.

Same production capacity

The slide states:

FEtOH = 100 kg ethanol/h

Three cases are compared:

1. Batch fermentation
2. Continuous microfiltration with dilution rate Di = 0.2 h⁻¹
3. Continuous microfiltration with dilution rate Di = 1 h⁻¹

Reactor volumes

The slide gives approximate reactor volumes:

• Batch: 35.9 m³
• Continuous MF, Di = 0.2 h⁻¹: 11.9 m³
• Continuous MF, Di = 1 h⁻¹: 2.4 m³

Interpretation

Higher dilution rate means liquid passes through the system faster. If productivity is maintained, the reactor volume can be smaller.

So:

Batch needs the largest reactor. Continuous MF at high dilution rate needs the smallest reactor.

However, smaller reactor volume does not automatically mean cheaper total process, because membrane area and pumps may become much more expensive.

Slide 32 — Fermentation case: project questions

This slide lists the tasks for the fermentation mini-project.

You need to answer:

1. Draw detailed P&IDs with relevant sensors.
2. Dimension fermenters.
3. Define pump requirements for membrane operation.
4. Choose materials.
5. Choose valves and pumps.
6. Estimate process cost and feasibility.
7. Identify how costs are split between CAPEX, membrane operation, etc.

What this means

The project is not only about calculations. It is about process design.

You need to think like an engineer:

• What equipment is needed?
• What sensors control the process?
• What assumptions are made?
• What costs dominate?
• Which design is most favorable?

Slide 33 — Fermentation case: membrane process

This slide gives the membrane assumptions.

Membrane job

The membrane retains microorganisms while allowing product and byproducts to leave.

So cells stay in the fermenter, while ethanol-containing permeate exits.

Membrane permeability

The slide gives:

Permeability = 80 L m⁻² h⁻¹ bar⁻¹

This means that for every square meter of membrane area, each bar of pressure gives 80 L/h of filtrate.

Desired flux

The desired flux is:

40 LMH

LMH means:

L m⁻² h⁻¹

So each square meter of membrane should produce 40 L/h permeate.

Transmembrane pressure

The slide says this requires:

TMP = 0.5 bar

Because:

80 LMH/bar × 0.5 bar = 40 LMH

Crossflow mode

The membrane operates in crossflow mode. Liquid flows along the membrane surface, which helps reduce fouling.

Assumptions:

• pressure drop from feed inlet to retentate outlet = 0.2 bar,
• crossflow velocity = 2 m/s,
• crossflow = 10 m³/h per m² membrane area.

Tasks

You must calculate:

• required membrane area,
• required pumps,
• pump head and flow,
• pump price,
• electricity consumption.

Slide 34 — Fermentation case: membrane area

This slide gives the required membrane areas.

Formula idea

Required membrane area is calculated from:

Area = permeate flow / flux

If you need a large permeate flow and flux is fixed, you need more membrane area.

Results

The slide gives:

• Batch: A = 0 m²
• Continuous MF, Di = 0.2 h⁻¹: A = 22.4 m²
• Continuous MF, Di = 1 h⁻¹: A = 222.4 m²

Interpretation

Batch has no membrane, so membrane area is zero.

The high dilution-rate continuous case needs much more membrane area because much more liquid must be filtered per hour.

Key lesson

A smaller reactor can require a much larger membrane system.

This is an important engineering tradeoff:

Smaller tank ≠ automatically cheaper process.

Slide 35 — Fermentation case: required pumps

This slide calculates pump flow and head for the membrane process.

Crossflow assumption

The slide states:

10 m³/h is needed per m² membrane area

So pump flow is:

Q = 10 m³/h/m² × membrane area

For Di = 0.2 h⁻¹

Membrane area:

22.4 m²

Pump flow:

Q = 10 × 22.4 = 224 m³/h

Pump head:

6 m

Suggested setup:

• 2 pumps,
• each CRE 125-1-1,
• each provides 112 m³/h and 6 m head.

For Di = 1 h⁻¹

The slide appears to have a typo where it repeats “Cont MF Di = 0.2” for the second case, but based on the membrane area 222.4 m², this must refer to Cont MF Di = 1 h⁻¹.

Membrane area:

222.4 m²

Pump flow:

Q = 10 × 222.4 = 2224 m³/h

Suggested setup:

• 20 pumps,
• CRE 125-1-1,
• each 3.346 kW.

Why so many pumps?

Because crossflow filtration requires high recirculation flow to keep the membrane surface clean and reduce fouling.

The high dilution-rate case needs a much larger membrane and therefore a much larger crossflow pump capacity.

Slide 36 — Fermentation case: pump energy

This slide estimates pump electricity consumption.

For Di = 0.2 h⁻¹

From the previous slide:

• 2 pumps,
• each uses energy corresponding to 1070 EUR/year.

Total:

2140 EUR/year

For Di = 1 h⁻¹

• 20 pumps,
• each uses energy corresponding to 1070 EUR/year.

Total:

21,400 EUR/year

Key lesson

The membrane system does not only add equipment cost. It also adds operating cost because pumps must run continuously.

Engineering interpretation

The high dilution-rate case has a small reactor, but pump energy becomes much larger because the required membrane area and crossflow are much larger.

Slide 37 — Fermentation case: repeated project questions

This slide repeats the overall project questions.

That repetition is useful because the membrane calculations are only one part of the design.

You still need to connect:

• P&ID,
• sensors,
• reactor sizing,
• pump sizing,
• material choices,
• valve choices,
• CAPEX,
• OPEX,
• feasibility.

Important takeaway

A good design report should not only present numbers. It should explain why the chosen process is technically and economically reasonable.

Slide 38 — CAPEX reactors

This slide calculates reactor capital costs.

CAPEX meaning

CAPEX means capital expenditure, which is the upfront cost of buying and installing equipment.

Reactor volume comparison

From earlier:

• Batch reactor volume: 35.9 m³
• Continuous MF Di = 0.2 h⁻¹: 11.9 m³
• Continuous MF Di = 1 h⁻¹: 2.4 m³

Cost trend

Smaller reactor volume gives lower reactor cost.

The later cost table gives:

• Batch reactor cost: 632,000 USD
• Cont MF Di = 0.2 h⁻¹ reactor cost: 297,000 USD
• Cont MF Di = 1 h⁻¹ reactor cost: 127,000 USD

Interpretation

Continuous fermentation reduces reactor CAPEX because reactor volume is smaller.

But again, this does not include membrane and pump costs yet.

Slide 39 — CAPEX membrane system pumps

This slide adds pump purchase costs.

Batch

Batch has no membrane system.

Pump cost:

0 USD

Cont MF Di = 0.2 h⁻¹

Requires:

• 2 pumps,
• each costs 20,000 USD.

Total:

40,000 USD

Cont MF Di = 1 h⁻¹

Requires:

• 20 pumps,
• each costs 20,000 USD.

Total:

400,000 USD

Interpretation

The high dilution-rate process has the smallest reactor, but the pump system becomes very expensive.

This is the central tradeoff:

Increasing dilution rate reduces reactor size but increases membrane and pump demand.

Slide 40 — OPEX

OPEX means operating expenditure.

This slide identifies two main operating costs for the membrane system:

1. Membrane replacement
2. Pump electricity consumption

Why OPEX matters

A process with low CAPEX may still be expensive if yearly operating costs are high.

In membrane systems, OPEX is especially important because:

• membranes foul and need replacement,
• pumps consume electricity continuously,
• maintenance is required.

Slide 41 — Costs of membrane replacement

This slide calculates yearly membrane replacement cost.

Given assumptions

Membrane cost:

790 USD/m²

Membrane lifetime:

5 years

Membrane areas:

• Batch: 0 m²
• Cont MF Di = 0.2 h⁻¹: 22.4 m²
• Cont MF Di = 1 h⁻¹: 222.4 m²

Batch

No membrane:

0 USD/year

Cont MF Di = 0.2 h⁻¹

Membrane cost:

22.4 × 790 = 17,696 USD

Yearly cost over 5 years:

17,696 / 5 = 3,539 USD/year

Cont MF Di = 1 h⁻¹

Membrane cost:

222.4 × 790 = 175,696 USD

Yearly cost over 5 years:

175,696 / 5 = 35,139 USD/year

Interpretation

The high dilution-rate continuous system has about 10 times more membrane area and therefore about 10 times higher membrane replacement cost.

Slide 42 — Costs of electricity for membrane pumps

This slide converts pump electricity consumption into yearly cost.

Given assumption

Each pump consumes electricity corresponding to:

1070 EUR/year = 1225 USD/year

Batch

No membrane pumps:

0 USD/year

Cont MF Di = 0.2 h⁻¹

2 pumps:

2 × 1225 = 2450 USD/year

Cont MF Di = 1 h⁻¹

20 pumps:

20 × 1225 = 24,500 USD/year

Interpretation

Pump electricity cost scales with number of pumps.

The high dilution-rate process has 10 times more pumps than the lower dilution-rate process, so electricity cost is also 10 times higher.

Slide 43 — Total costs

This slide combines CAPEX and OPEX.

CAPEX comparison

OPEX comparison

Total cost over 30-year lifetime

The slide gives annualized total cost of operation:

• Batch: 52,667 USD/year
• Cont MF Di = 0.2 h⁻¹: 51,774 USD/year
• Cont MF Di = 1 h⁻¹: 279,257 USD/year

Main conclusion

The Cont MF Di = 0.2 h⁻¹ case is slightly cheaper than batch in annualized cost.

The Cont MF Di = 1 h⁻¹ case is much more expensive because membrane area, pumps, and operating costs become very large.

Engineering lesson ⚙️

The most intensified process is not always the most economical.

Higher dilution rate gives:

• smaller reactor,
• but much higher membrane area,
• much higher pump CAPEX,
• much higher electricity,
• much higher membrane replacement cost.

Slide 44 — Advice for mini report

This slide gives practical report-writing advice.

What to do

Make assumptions clearly

For example:

• membrane lifetime = 5 years,
• pump cost = 20,000 USD each,
• maintenance = 5% of CAPEX/year,
• flux = 40 LMH.

Assumptions are not bad, but they must be stated clearly.

Set boundaries

A mini report should not cover everything. Define what is included and what is excluded.

For example:

• include reactor and pump CAPEX,
• include membrane replacement and electricity,
• exclude labor, cleaning chemicals, downtime, installation complexity, etc.

Keep it 5–10 pages

The report should be focused and concise.

What not to do

Do not write too much

More text does not automatically mean better analysis.

Do not ask for quotes

The slide likely means that for the mini-project, you should estimate based on available data rather than contacting suppliers for detailed commercial quotes.

Slide 45 — Workshop day, May 6th

This slide gives the schedule for the workshop day.

Chemical engineering students

• 8:15–12:00: Practical control exercise with Kirsten
• 12:30–16:15: Support from Mads on the mini project

Biotechnology students

• 8:15–12:00: Support from Mads on the mini project
• 12:30–16:15: Practical control exercise with Kirsten

Meaning

The day is split between practical control training and mini-project support.

Overall summary of the whole lecture

This lecture teaches how different sensors are used in process systems and how sensor choice depends strongly on the process conditions.

Sensor selection is about tradeoffs

No sensor is perfect.

For example:

• Venturi meters are simple but cause pressure loss.
• Vortex meters work for clean liquids but not particles or bubbles.
• Electromagnetic meters are good for conductive suspensions but not demineralized water.
• Ultrasonic meters are good for large pipes but disturbed by bubbles and particles.
• Mass flowmeters are very precise but expensive.

Temperature sensors also involve tradeoffs

• Thermocouples are fast and simple but less precise.
• RTDs are precise and stable but slower and more expensive.
• 4-point measurement and Wheatstone bridges improve accuracy.

Pressure and level sensors are closely connected

Pressure can be used directly for pressure measurement or indirectly for liquid level measurement.

For example:

• differential pressure can estimate tank level,
• pneumatic bubbling works well for dirty liquids,
• ultrasonic level sensing avoids direct contact but struggles with foam and dust.

pH measurement is powerful but maintenance-heavy

pH electrodes are essential in fermentation and chemical processing, but they are fragile and require calibration, temperature compensation, and electrolyte maintenance.

The fermentation case shows real engineering decision-making

The continuous membrane fermentation system can reduce reactor size, but it creates new costs:

• membrane area,
• pump capacity,
• pump electricity,
• membrane replacement,
• maintenance.

The best option in the given calculation is not the most aggressive continuous process. Instead, continuous MF at Di = 0.2 h⁻¹ gives the lowest annualized cost, slightly below batch, while Di = 1 h⁻¹ becomes too expensive due to membrane and pump demands.

Big takeaway 🧠

A good process design does not only ask:

“Can we make the reactor smaller?”

It also asks:

“What extra equipment, sensors, energy, maintenance, and cost does that require?”