Chapter 7: Sustainable engineering applications for process industries Flashcards
What are categories of pollution prevention for unit operations?
- Material
selections and substitutions
– Chemical reactors
– Separators and heat exchangers
– Fugitive emissions
– Storage, transport and loading/unloading operations
What are examples of pollution prevention in industrial processes?
-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
What do chemical reactors do?
Chemical reactors convert raw materials into desired products.
What is an environmental concern about chemical reactors and how will improving the performance of the reactor help the environment?
-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.
What are the general measures of performance for chemical reactors?
-Conversion
-Selectivity
-Yield
-Atom Economy
Define conversion
How much feed is converted
What is selectivity?
How much converted feed becomes the
product
Yield
How much product collected for each unit of
feed into the reactor
What is atom economy?
the ratio of the molecular weight of
the desired product and the molecular weight of all
materials generated from the transformation
What are general approaches for improving the performing of a chemical reactor?
-Maximize atom economy in the design
of a reaction pathway
- Maximize selectivity toward the desired
product
What property difference does distillation/absorption exploit?
Vapor pressure
What property difference does adsorption use?
Chemical and physical surface sorption
What property difference does condensation use?
Boiling point
What property
difference do membranes use?
Diffusivity and solubility
What propery difference do reverse osmosis/micro-and ultrafiltration use?
Molecular size
What property difference does crsytallization use?
Melting point
What property difference does liquid-liquid extraction use?
Distribution between immiscible phases
What property does sedimentation exploit?
Particle size and density
What are options for waste minimization from unit operations?
- 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
How much do fugitive emissions from synthetic organic chemical manufacturing industry facilities account for?
1/3 of the total organic emissions.
How can fugitive emissions be reduced?
-Regularly
monitoring and maintaining facilities. Greater frequency = more emissions reduction
-Reduce the number of equipment components
- Replace low quality components with high
quality components
How does leaking result from connectors?
Leaking mainly results from
aging and damage of the flange gaskets
after exposure to high temperature/pressure
and corrosive fluids environment.
Where does leaking come from when it comes to valves?
Leaking mostly comes from the movable stem
due to the worn or damaged packing sealant.
Where does leaking come from when it comes to pumps and compressors?
Leaking comes from the
sealing surrounding the pump or compressor shaft.
How to prevent leaks from valves?
Use high quality valves with dual-packing or dual valves.
– Use leakless valves like bellow and diaphragm valves in
places with little tolerance
How to prevent leaks from pumps and compressors?
Use packing sealant, mechanical seal, tandem seal and double
seal and the leakless diaphragm pump.
How to prevent leaks from pressure relief devices?
Use rupture disks rather than relieve valves.
How to prevent open-ended valves and lines from leaking?
Install pipe plugs, caps or blind flanges, dual-valves.
What are some common equipment that can be modified to reduce fugitive emissions?
-Connectors
-Valves
-Pumps and compressors
-Pressure relief devices
-Open-ended valves and lines
-Sampling systems
What are some options for minimizing waste/emissions from storage tanks?
-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.
What are some options for minimizing wastes/emissions from loading/unloading operations?
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
Which type of recycling is favoured to reduce the impact associated with waste handling and transportation?
On-site recycling
What are the four principles of natural ecosystems?
- Roundput
- Diversity
- Locality
- Gradual changes
Explain the “roundput” principle of natural ecosystems
Waste equals food, and the only input to the
system is the solar energy from the sun.
Explain the “diversity” principle in natural ecosystems
Ecosystem survival is based on diversity,
diversity in species, in organisms, in interdependency, in
“cooperation” and in information.
Explain the “locality” principle in natural ecosystems?
The “actors” in the ecosystem adapt to the local
environmental conditions and cooperate with their
surroundings in diverse interdependent relationships.
Explain the “gradual changes” principle in natural ecosystems?
Ecosystem survival relies on the flow
resource from the sun, and the evolution respects the
renewal rate of the ecosystem.
How would an ideal industrial ecosystem be constructed?
The system would be constructed from two
systems: the industrial subsystem and the natural/mother
ecosystem in which the industrial ecosystem is embedded.
What would be the only input and output to the ideal industrial ecosystem AS A WHOLE?
Input: Solar energy
Output: Waste heat
What would be the inputs to the industrial system in the ideal industrial ecosystem?
The renewable resources and recycling of matter as
cascading of energy would then happen between the
industrial actors of the system.
What would be the outputs from the industrial system to the natural system in an ideal industrial ecosystem?
Only such things that nature can tolerate or
perhaps re-use and recycle in its own operation.
What are the important goals of food webs analysis?
-To study the flows of resources in ecosystems
-To analyze ecosystems for dynamic interactions
Why are food web studies in biological systems formed?
They are formed as opportunistic
responses to local
resource
availability and
desirability.
What is species richness?
The number of different types of
organisms within the system
What is connectance?
Degree of interactions
What does metabolic analysis focus on and what is identified as a result of the analysis?
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.
What is the emphasis of elemental flow analysis?
The atom (Ex. gold, silver, lead)
What is the emphasis of molecular flow analysis?
Focus on molecules
What are disadvantages and obstacles to eco-industrial parks (EIPs)?
-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.
How can pollution prevention be implemented for chemical reactors?
- 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
How can pollution prevention be achieved in chemical processes?
By optimizing the energy and matrial
efficiency of individual unit operations.
What are ways to prevent pollution in separation units?
-Selection of suitable separation process
– Enhancing separation efficiency and energy efficiency
– Minimizing the sludge generation from reboilers
– Prolonging the operation of separation units.
What are potential opportunities for eco-industrial parks?
-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
How can secondary emissions be reduced?
-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.
