A2 - Quantitative indicators for energy, water and raw material use: Mass Balances

What can the food production chain be used for?

• To use raw material efficiently

• See where water is consumed

• See where energy is consumed.

Law of conservation of mass

Mass can be neither created nor destroyed

Mass balance formula

Accumulation = in - out + production

Accumulation = change in time

• No change in time? → accumulation = 0

Batch

No input and output

• In and out are 0

• Accumulation = production

Semi-batch

Periodically adding (input) or removing (output)

Continuous

Continuous input and output throughout the process

What does it mean if a process has no conversion?

Then production = 0

Steady state

When process variables (e.g. T, flow rate) are independent of time this happens in continuous processes, because there is no accumulation of products.

Continuous steady-state process without production?

• Accumulation = 0 because production = 0

• In = out

Transient

Process variables that change in time

mass fraction formula

Mass of the compound divided by the total mass of the material

Mass fraction vs mass ratio

• In case of air kg water per kg dry air is used

• Therefore a ratio is used

Reasons to apply recycle streams

• To increase the yield from a chemical reaction

• To conserve energy

  • Recycling of air in a dryer

• To reduce the inlet concentration of an ingredient

  • Moisture content in a feed of a dryer.

Reasons to apply bypass

• Reduce size unit operation

• Product quality

• Safety measure

Heating

Direct & Indirect heating

• Direct: Having direct contact between the heat source (e.g. steam) and the product

  • Steam injection

  • Batch process

• Indirect

  • Heat exchangers

  • Plate, tubes and pipes, scraped surfaces

  • Continuous process

Indirect heating

• Heating exchangers

  • Plate

    • More thin and larger walls is better & more efficient

  • Tubes and pipes

  • Or scraped surfaces (for e.g. crystals)

Evaporation

Removing water from a liquid feed to produce a concentrated liquid product

e.g.:

• Fruit juices (orange juice concentrate)

• Vegetable juices (tomato pastes and purees)

• Dairy products (condensed milk)

Sankey diagrams

• Visualizing energy or mass flows

• Conservation of mass or energy

• Representation of flow by arrows

• Arrow width = scale factor * M

  • Width of the arrow is related to the size of the stream

  • For mass, energy, all conserved quantities

• All flows in go into the same side

• All flows out go into the opposite side

• For conserved variables, cumulative in should be equal to cumulative out

Golden rules for Sankey diagrams

• Main input (raw material) usually in at the left side

• Main output (product) usually out at the right side

• Waste (unwanted output) goes down, emissions go up

• Clear and short name to each process step

• Color for different components

• Short label to all arrows.