Chapter 7: Sustainable engineering applications for process industries

Question 1

What are categories of pollution prevention for unit operations?

Answer 1

• Material
  selections and substitutions
  – Chemical reactors
  – Separators and heat exchangers
  – Fugitive emissions
  – Storage, transport and loading/unloading operations

Question 2

What are examples of pollution prevention in industrial processes?

Answer 2

-Use of less hazardous materials and design of
safer/benign chemicals

-Use of high quality raw materials with less
impurities or elimination of feedstock impurities

Question 3

What do chemical reactors do?

Answer 3

Chemical reactors convert raw materials into desired products.

Question 4

What is an environmental concern about chemical reactors and how will improving the performance of the reactor help the environment?

Answer 4

-Wastes or byproduct may be produced and
propagate into downstream processing units.
-Improving the chemical reactors’
performance will directly lead to the reduction or
elimination of waste streams.

Question 5

What are the general measures of performance for chemical reactors?

Answer 5

-Conversion
-Selectivity
-Yield
-Atom Economy

Question 6

Define conversion

Answer 6

How much feed is converted

Question 7

What is selectivity?

Answer 7

How much converted feed becomes the
product

Question 8

Yield

Answer 8

How much product collected for each unit of
feed into the reactor

Question 9

What is atom economy?

Answer 9

the ratio of the molecular weight of
the desired product and the molecular weight of all
materials generated from the transformation

Question 10

What are general approaches for improving the performing of a chemical reactor?

Answer 10

-Maximize atom economy in the design
of a reaction pathway
- Maximize selectivity toward the desired
product

Question 11

What property difference does distillation/absorption exploit?

Answer 11

Vapor pressure

Question 12

What property difference does adsorption use?

Answer 12

Chemical and physical surface sorption

Question 13

What property difference does condensation use?

Answer 13

Boiling point

Question 14

What property
difference do membranes use?

Answer 14

Diffusivity and solubility

Question 15

What propery difference do reverse osmosis/micro-and ultrafiltration use?

Answer 15

Molecular size

Question 16

What property difference does crsytallization use?

Answer 16

Melting point

Question 17

What property difference does liquid-liquid extraction use?

Answer 17

Distribution between immiscible phases

Question 18

What property does sedimentation exploit?

Answer 18

Particle size and density

Question 19

What are options for waste minimization from unit operations?

Answer 19

• Improve separation efficiencies

-Reduce waste generation from reboiler

– Insulate or preheat the column feed to reduce the load on the
reboiler.

– Reduce pressure drop over the column or reduce the pressure
in the distillation column (vacuum distillation) to lower the
load on the reboiler.

– Reduce fouling by the use of on-line cleaning techniques,
antifoulants, specially designed heat exchange tubes or heat
exchangers.

– Improve cleaning techniques for heat exchangers

– Redesign of the reboiler to avoid the unnecessary shut-down.

• Good process control and maintenance to avoid
  unstable operation

Question 20

How much do fugitive emissions from synthetic organic chemical manufacturing industry facilities account for?

Answer 20

1/3 of the total organic emissions.

Question 21

How can fugitive emissions be reduced?

Answer 21

-Regularly
monitoring and maintaining facilities. Greater frequency = more emissions reduction

-Reduce the number of equipment components

• Replace low quality components with high
  quality components

Question 22

How does leaking result from connectors?

Answer 22

Leaking mainly results from
aging and damage of the flange gaskets
after exposure to high temperature/pressure
and corrosive fluids environment.

Question 23

Where does leaking come from when it comes to valves?

Answer 23

Leaking mostly comes from the movable stem
due to the worn or damaged packing sealant.

Question 24

Where does leaking come from when it comes to pumps and compressors?

Answer 24

Leaking comes from the
sealing surrounding the pump or compressor shaft.

Question 25

How to prevent leaks from valves?

Answer 25

Use high quality valves with dual-packing or dual valves. – Use leakless valves like bellow and diaphragm valves in places with little tolerance

Question 26

How to prevent leaks from pumps and compressors?

Answer 26

Use packing sealant, mechanical seal, tandem seal and double seal and the leakless diaphragm pump.

Question 27

How to prevent leaks from pressure relief devices?

Answer 27

Use rupture disks rather than relieve valves.

Question 28

How to prevent open-ended valves and lines from leaking?

Answer 28

Install pipe plugs, caps or blind flanges, dual-valves.

Question 29

What are some common equipment that can be modified to reduce fugitive emissions?

Answer 29

-Connectors -Valves -Pumps and compressors -Pressure relief devices -Open-ended valves and lines -Sampling systems

Question 30

What are some options for minimizing waste/emissions from storage tanks?

Answer 30

-Using mixers and emulsifying agent to reduce tank bottoms which are sludge accumulating at the bottom of large storage vessels. * Vapor-recovery devices that trap and condense escaping vapors for return to the tank can be used to reduce emissions from fixed-roof storage tanks. * Breathing losses can be prevented by using variable-vapor-space tanks with a telescoping roof or a flexible diaphragm or by floating a roof on the surface of the liquid in the tank.

Question 31

What are some options for minimizing wastes/emissions from loading/unloading operations?

Answer 31

Using off-loading devices to completely empty shipping containers -Using dedicated service containers to avoid cleaning residual materials - Using reusable containers - Using appropriate-sized containers

Question 32

Which type of recycling is favoured to reduce the impact associated with waste handling and transportation?

Answer 32

On-site recycling

Question 33

What are the four principles of natural ecosystems?

Answer 33

1. Roundput 2. Diversity 3. Locality 4. Gradual changes

Question 34

Explain the "roundput" principle of natural ecosystems

Answer 34

Waste equals food, and the only input to the system is the solar energy from the sun.

Question 35

Explain the "diversity" principle in natural ecosystems

Answer 35

Ecosystem survival is based on diversity, diversity in species, in organisms, in interdependency, in “cooperation” and in information.

Question 36

Explain the "locality" principle in natural ecosystems?

Answer 36

The “actors” in the ecosystem adapt to the local environmental conditions and cooperate with their surroundings in diverse interdependent relationships.

Question 37

Explain the "gradual changes" principle in natural ecosystems?

Answer 37

Ecosystem survival relies on the flow resource from the sun, and the evolution respects the renewal rate of the ecosystem.

Question 38

How would an ideal industrial ecosystem be constructed?

Answer 38

The system would be constructed from two systems: the industrial subsystem and the natural/mother ecosystem in which the industrial ecosystem is embedded.

Question 39

What would be the only input and output to the ideal industrial ecosystem AS A WHOLE?

Answer 39

Input: Solar energy Output: Waste heat

Question 40

What would be the inputs to the industrial system in the ideal industrial ecosystem?

Answer 40

The renewable resources and recycling of matter as cascading of energy would then happen between the industrial actors of the system.

Question 41

What would be the outputs from the industrial system to the natural system in an ideal industrial ecosystem?

Answer 41

Only such things that nature can tolerate or perhaps re-use and recycle in its own operation.

Question 42

What are the important goals of food webs analysis?

Answer 42

-To study the flows of resources in ecosystems -To analyze ecosystems for dynamic interactions

Question 43

Why are food web studies in biological systems formed?

Answer 43

They are formed as opportunistic responses to local resource availability and desirability.

Question 44

What is species richness?

Answer 44

The number of different types of organisms within the system

Question 45

What is connectance?

Answer 45

Degree of interactions

Question 46

What does metabolic analysis focus on and what is identified as a result of the analysis?

Answer 46

Metabolic analysis focuses on what enters a facility/system, what leaves, and to what degree entering material is utilized usefully or is lost. Opportunities for substantially improving environmental performances can often be identified.

Question 47

What is the emphasis of elemental flow analysis?

Answer 47

The atom (Ex. gold, silver, lead)

Question 48

What is the emphasis of molecular flow analysis?

Answer 48

Focus on molecules

Question 49

What are disadvantages and obstacles to eco-industrial parks (EIPs)?

Answer 49

-Inflexibility in the use of resources -Uncertainty in the supply of raw materials -Obstacles to technological innovations -Limits imposed by the management, funds, organization etc.

Question 50

How can pollution prevention be implemented for chemical reactors?

Answer 50

- Selection of less toxic and high quality raw materials – Pre-purification of raw materials – Optimization of selectivity and conversion – Recycling of unconverted raw materials – Development of new catalyst for new reaction pathways

Question 51

How can pollution prevention be achieved in chemical processes?

Answer 51

By optimizing the energy and matrial efficiency of individual unit operations.

Question 52

What are ways to prevent pollution in separation units?

Answer 52

-Selection of suitable separation process – Enhancing separation efficiency and energy efficiency – Minimizing the sludge generation from reboilers – Prolonging the operation of separation units.

Question 53

What are potential opportunities for eco-industrial parks?

Answer 53

-Build EIPs to make optimal use of mass flux, energy flux and information flux – EIPs can promote green development via developing green links between industries or groups of industries – EIPs can create R&D opportunities for new processes and equipments

Question 54

How can secondary emissions be reduced?

Answer 54

-Alteration of waste treatment equipment – Pretreatment of the waste streams to remove VOCs – Modification of waste streams. – Switch from conventional “dirty” fuels to “clean” and/or renewable fuel sources – Combustion modifications.