1. POLLUTION PREVENTION AND UNIT OPERATIONS
CHAPTER 8
POLLUTION PREVENTION AND UNIT OPERATIONS

2. UNIT OPERATIONS AND POLLUTION PREVENTION
Chemical Reactors
Separation Devices
Separative Reactors
Storage Tanks and Fugitive Sources
Narration : These topics will be discussed over the course of this chapter, specifically relating them to pollution prevention.
A careful evaluation of the mechanisms of in-process waste generation can direct the process designer toward environmentally material choices and other pollution prevent options.
The operating conditions of each unit operation/process should be optimized in order to achieve maximum reactor conversion and separation efficiencies. The best material storage and transfer technologies should be considered in order to minimize releases of materials to the environment.
Chemical Reactors (material use and selection, feedstocks, solvents, catalysts, reaction type and reactor choice, reactor temperature, mixing)
Separation Devices (mass separating, distillation, adsorption, reverse osmosis)
Separative Reactors
Storage Tanks and Fugitive Sources (reducing emmisions, sources)

3. Pollution Prevention for Chemical Reactors
In the designing of chemical reactors for pollution prevention there are important considerations :
Raw materials, products and byproducts
Conversion yield and selectivity for the desired product
To establish reaction type and make the reactor choice
Definition of the reactor operation
Narration : Raw materials, products and byproducts should no or relatively low environmental and toxicological (health) impact potential. The conversion and selectivity of reactants to desired products should be high and their conversion towards byproducts should be low. If byproducts are generated, immediate separation or isolation should be considered in order to avoid problems further down the production line. It is also easier to handle these by-products by their phisicochemical properties if they are not handled individually (separately). The mean target in an industrial chemical process encompasses yield and selectivity, which relates to the process’s efficiency. A more efficient process leads to many benefits, usually economical, but in the case of pollution prevention, includes environmental benefits. Establishing the reaction type (reversilbe or irreversible) is also essential to determine the type of reactor to be used. Also, the reactor operation is detemined by the type of reactor and reaction.

4. Selection of Reactors and Material Selection
The selection of materials has an influence on the environmental impacts caused by reactors in chemical processes.
For materials used in a reactor it is important to consider :
The choice of feed entering the reactor
The catalyst (if one is needed)
Solvents or diluents
Narration : the following slides will discuss some of the different criterias in the material selection

5. Selection of Reactors and Material Selection
Raw Materials and Feedstocks
Raw materials and feedstocks used in chemical processes should not pose toxic threats to the environment or to human health.
New process chemistry may need to be adopted if raw materials are eliminated or substituted.
If toxic compounds are being used, they should be replaced with an equivalent, but less toxic, substance.
Narration : In order to assess the environmental impact of the materials, one needs to check their toxicological and safety properties, and the ease at which it can be handled. The toxicological properties can be found on the substance’s MSDS (material safety data sheet). If MSDS sheets are not redily available, toxicological levels can be found in environmental federal regulations or laws. Dangerous raw materials should be replaced with an alternative having properties such that the material will contribute to less waste generation, be easy to handle and yield more of the desired product versus by-products. Also, the generation of by-products and intermediates in the process should be of minimal toxic levels.

6. Selection of Reactors and Material Selection
Solvents
Solvents are very useful and important in the chemical process and due to their high volatility cause :
Tropospheric (low-level) ozone occuring from smog
Health concerns for workers
Health concerns for the general population in the vicinity of the facility
Narration : Solvents are an important raw material in a reactor. They are used in reactions of polymerization of solutions or emulsions. In some polimerization reactions, solvents are used for the precipitation of the polymer into solid form, for the co-solubilization of the monomers and as initiators. Examples of such solvents include : xylene, methanol, lubricant oil, hexane, heptane and water. It is very important to consider the by-products that may be generated when solvents are used. The solvents used for the cleaning of equipments and/or machinery must also be considered. If a solvent poses a large environmental and/or health risk, it should be substituted with on that have lesser impacts. There exist several on-line resources for evaluating substitute solvents. For example, the solubility, toxicological, cost and environmental properties of the candidate solvents can be compared with each other and with the original solvent in order to determine the most appropriate choice.

7. Selection of Reactors and Material Selection
Solvent Selection
Some criteria to consider for solvent selection :
The solvent’s properties
The byproducts generated and their properties
The potential health impacts to the workers and to the general population
The potential environmental repercussions

8. Selection of Reactors and Material Selection
Catalysts
Catalyst : a substance that is added to a chemical reaction mixture in order to accelerate the rate of reaction.
Type of Catalysts :
homogeneous, which is one phase with the reaction mixture
heterogeneous, which exists in a phase other then the reacting mixture, (typically existing as a solid within a reacting fluid mixture)
Narration : As you know, a catalyst speeds up the rate of the reaction and can also encourage the reaction to be more selective towards one product. In general, the decision to use a catalyst (and what type of catalyst) is based on the type of chemical reaction (usually it is to speed up a slow chemical reaction).

9. Selection of Reactors and Material Selection
Benefits of Catalysts
Allow the use of more environmentally benign raw materials
Directly create more environmentally acceptable products from reactions
Increases selectivity toward the desired product and away from unwanted byproducts (wastes)
Converts waste chemicals into raw materials
Narration : In general the catalyst has a benign environment impact because achieves high eficiency in the use of materials and in the control of processes.

10. Selection of Reactors and Material Selection
Catalyst Selection
Important considerations regarding catalyst selection include :
- End disposal of the catalyst
- The possiblity of regenerating it
Because these two issues may have important environmental impacts, it is desirable to regenerate the catalyst as many times as possible and /or use minimal energy or materials to regenerate it instead of disposing of it.
Narration : Many caracteristics exist that affect the choice of a catalyst. By comparing the value (both economical and environmental) of regenerating the catalyst versus disposing of it. Regenerating a catalyst can pose an environmental problem because it’s efficiency decreases with time (as it is used in a continuous process).

11. Selection of a Reactor : Reaction Type and Reactor Choice
Features that influence pollution prevention opportunities and strategies for selecting a chemical reactor :
Chemical reaction mechanism
The reaction order
Series or parallel reaction pathways,
Reversiblity
These details will determine the optimum reactor temperature, residence time, and mixing.
Narration : The chemical reaction mechanism is, in almost all cases, known for the reaction being studied. The mechanism helps to determine what are the slow and fast steps in the reaction. It sets the most important steps to control in the reactor and the residence time of the material in the reactor. The mechanism shows all the chemical compounds generated in the reactor or reaction, passing through the intermediates which makes it possible to determine potential hazards associated with the different substances produced (that are not the product) during the reaction. The reaction order also helps to know the time of reaction or residence of the material in the reactor.

12. Selection of a Reactor : Reaction Type and Reactor Choice
As a general rule, a desirable reaction includes :
A very high conversion of the reactants
High selectivity toward the desired product
Low selectivity toward any byproducts.
Narration : Yields and selectivity values that are very close to unity (value of one) indicate an efficient reaction, with little waste generation or reactants to separate in downstream unit operation (less additional unit operations).

13. Conversion and Selectivity Equations
Reactant conversion (reaction yield): ratio of the existing concentration of product to inlet reactant:
R P
[P] / [R]o
Reaction selectivity: ratio of existing product concentration to the undesired byproduct concentration
R P + W
[P] / [W]
Modified Selectivity is the ratio of exiting product concentration to the sum of product and byproduct (waste) concentrations:
[P] / ([P]+[W]) = [P] / [Reactant consumed]
Narration : Is desired that all the raw material (inlet reactant) is converted to the main product

14. Types of Reactions
Parallel reactions pathways are very common in the chemical industry. These kind of reactions are in competition of the main reactions (undesirable).
R P
R W
Also series reactions, it’s when a reaction is followed of other one, consecutively (one after other).
R P W kp kw
Narration : An example of an industrial parallel reaction is the partial oxidation of ehtylene to ethylene oxide, where the parallel reaction converts ethylene to carbon dioxide an water, the byproducts. In almost all cases, parallel reactions are undesirable for environment. In serial reactions, longer reactor residence times lead to more product formation but also lead to more byproduct generation. The longer residence time should then be avoided. In these types of reactions, the rate of conversion of the first and second reactions must be known and considered in order to optimize the reactor residence time. This demonstrates that the selectivity is affected by reactor residence time, and therefore this parameter must also be considered for pollution prevention in chemical reactors.

15. Types of Reactions Optimizing the reaction in serial reactions:
* kp / kw must be as large as possible
* Control of the reaction residence time
kp and kw [=] reaction constants of product and waste respectively
Reversible reactions, are reactions where there is a competition between two reactions: one towards the desired product and the other one is of the decomposition of the product (in the opposite direction).
R P
This kind of reaction inhibits full conversion of reactants to products.
Narration : For longer residence times, the rate of waste generation is greater than rate of product formation. To minimize waste generation in series reactions, it is important to operate the reactor so that the ratio kp / kw is as large as possible and to control the reaction residence time. kp and kw are reaction constants of product and waste respectively. Also, another way to minimize byproduct generation is to remove the reaction product as it is being formed and before the its concentration builds up in the reactor. The removal of the byproducts should be immediate and they should be separated by their physical and chemical properties in order to avoid mixing them and avoid problems later on in additional unit operations.(as previously discussed).The reactor residence time is also a key to operating parameters for reversible reactions. Selectivity improvements for this type of reactions, operated at equilibrium, can be achieved by recycle to extinction (stream reforming). An example or reversible reaction is:
CH4 + H2O <--- CO + 3H2 which means CO emissions to the air. So is added an aditional condition of operating for reform the CO formed:
CO + H2O <--- CO2 + H2
There are more costs because requires additional operations for reform the undesired product, but the process is cleaner.

16. Types of Reactors
Continuous-flow stirred-tank reactor (CSTR), consists of a batch of reaction stirred at certain parameters settled.
Plug flow reactor, can be staged and each stage can be operated at different conditions to minimize waste formation
Fixed-bed catalytic reactor, that is used when hot spots are a problem for highly exotermic reactions (it will likely avoid the unwanted temperature excursions)
Narration : In a CSTR it is very important to note the efficiency of the stirring. There is a wide technology developed in order to select the type of stirrer for different kinds of raw materials. A CSTR is not always the best choice because it has the disadvantage of great waste generation. It is also hard to separate the undesired products generated in the tank. The Plug flow reactor can sometimes consist of a pipeline reactor. It simplifies the operations like an in-situ reaction and keeps the product continuously flowing towards the next stage of the process. For a reactor adequate temperature control is critical in reducing byproduct formation for reactions that are highly temperature-sensitive. When these types of reactions are necessary, a Fixed-bed catalytic reactor is used. In other words, when the temperture is the critical parameter in a reaction and hard to control homogeously, this is the ideal reactor.

17. Reaction Temperatures
Can influence the :
Degree of conversion of reactants to products
Product yield
Product selectivity
Temperature is changed above or below the initial temperature:
ΔT = + To or – To
Ratio of [product] / [byproduct] ≈ T (direct ratio)
Therefore pollution can be prevented in parallel (and also series) reactions by increasing reactor temperature generally
Narration : As in the previous slide explains, temperature is an important reaction parameter. There are reactions that are completely governed by the temperature at which they occur. The temperature provides the conditions of activation energy to lead the reaction. If the process or reactor has a very good temperature control all the parameters mentioned above will be optimized. When temperature is changed above or below the initial temperature, the ratio of product/byproduct increases with increasing temperature and decreases with decreasing temperature (direct ratio). Therefore pollution (or byproduct generation) can generally be prevented in parallel (and also series) reactions by increasing reactor temperature.
There are technology for control the temperature in the type of reactor to use and it should be considered to form part in the design of the reactor in order to decrease the byproducts generation. Must be considered the upper and lower values of T for avoid byproducts and the process must be always in that rank.

18. Mixing
It’s the addition of two or more raw materials into a reactor to assure contact or collisions occur between substances in order for the chemical reaction to occur.
This effect of mixing occurs for both :
- Homogeneous and heterogeneous reaction systems
- Batch or semi-batch reactors
Narration : Mixing is an operation that determines the homogeneous stirring in a reactor and assures the complete reaction of reactants. When a reactant in one inlet stream is added to another reactant that already exists in a well-stirred reactor, the course of complex multiple reactions can be affected by the intensity of the mixing in the vessel (reactor). This intensity is a function of the reaction conditions and the reaction order. In other words, the level of mixing is determined for the rate of reaction. If the rate of reaction is dependent on the concentration of raw materials, the mixing could be a very important.

19. Mixing The factors that influence/are affected by mixing are:
The reaction must be mixed instantaneously at a molecular level.
The rate of reaction can be reduced because of diffusional limitations between segregated elements of the reaction mixture.
Problems with imperfect mixing are particularly evident for rapidly reacting systems. In these situations, reactants are significantly converted to products and byproducts before mixing is complete.

20. Pollution Prevention for Separation Units
Separation tecnologies are one of the most important unit operations found in chemical processes :
As the mixtures and chemical reactions are not 100% efficient, it is necessary to separate chemical components from one another prior to subsequent processing steps.
Separation unit operations generate waste because:
The separation steps themselves are not 100% efficient
Require addtional energy input
Require waste treatment to deal with off-spec products
Narration : Feedstocks are often complex mixtures and chemical reactions are not 100% efficient, therefore, there is always a need to separate chemical components from one another prior to subsequent processing steps.

21. Choice of Mass Separating Agent
Pollution Prevention for Seperation Units
Choice of Mass Separating Agent
Selectin a mass seperation agent (chemical compound like solvent) is an important issue for pollution prevention in order to avoid:
Exposure to toxic substances for facility workers and consumers who use the final product.
Excessive energy consuption in the recovery of the solvent or other raw materials
Associated health impacts of the emitted criteria pollutants (CO, CO2, NOx, and SOx, particulate matter)
Narration : A proper selection of mass separating agent (chemical compound like solvent)is very important in pollution prevention. A poor choice may result in exposure of toxic substances not only for facility workers but also consumers who use the final. It may also lead to excessive energy consuption and the associated health impacts of the emitted criteria pollutants (CO, CO2, NOx, and SOx, particulate matter). The mass separating agent must not be toxic or difficult to eliminate of the process.

22. Choice of Mass Separating Agent
Pollution Prevention for Separation Units
Choice of Mass Separating Agent
Adsorption is when a chemical dissolved in a liquid or a gas phase will preferentially become immobilized on the surface of a solid matrix (adsorbent) packed with a column.
Separation and recovery of toxic metal ions from aqueous streams is one of the very important application of adsorption
Narration : The adsorption process involves the surface sorption difference between substances. This is the fundament of the phenomena of separating.

23. Operation Design and Operation Heuristics for Separation Technologies
Chemical process
WASTE
Air
Water
Soil
While it may be difficult or impossible to eliminate all waste streams, it is certain that wastes can be minimized by:
- Judicious choice of mass separating agent
Correct choice and sequencing of separation technologies
Careful control of system parameters during operation.
Narration : In a chemical process, there are waste streams leaving the process and entering the air, the water, and the soil compartments of the environment.

24. Minimizing Waste from Seperation Technologies
Making the correct choice of type of separating process (i.e.: adsorption, distillation, dialysis, etc.)
Considering several pollution prevention heuristics to guide the design of the flowsheet and operation of the units
Associating streams of the process by simmilar compositions
Avoidint the addition of chemical compounds to improve separation (i.e. corrososive), unless necessary
Narration : Making the correct choice of seperation units, based on the physical properties of the molecules to be separated, will lead to processes that generate less waste and use less energy per unit of product. After selecting the best separation technology, it is worth considering several pollution prevention heuristics to guide the design of the flowsheet and operation of the units. Streams of similar enough composition can be combined in order to reduce the number of unit operations and their associated capital costs and emission sources. Chemical compounds (i.e. corrososive) should never be added unless necessary and if added or generated in the process, should be separated immediately. Their removal can minimize investment and the generation of trace metals.

25. Minimizing Waste from Seperation Technologies Continued
Reduce as much as possible the number of components of simmilar component properties
When adding separating agents, remove it in the next step of the process of separation using an energy separating agent technology
The process should avoid separation technologies that operate far from ambient temperature and pressure.If large variations from ambient temperature are required, it is more economical to operate above rather than below.
Narration : If component properties are very close (resulting in a difficult separation) or product purity requirements from the separation are extremely high, reducing the number of components involved will make the separation easier. If mass separating agents need to be added, they should be removed (preferable recycled) in the next step of the process using an energy separating agent technology. The process should avoid separation technologies that operate far from ambient temperature and pressure because of encured costs and energy wastes. However, if variations from ambient temperature are required, it is more economical to operate above rather than below.

26. Types of Separation Technologies :
Distillation Columns
It is used for over 90% of the separation applications in chemical processing.
Distillation columns contribute to process waste in four ways:
By allowing impurities to remain in a product
By forming waste within the column itself
By inadequate condensing of overhead product
By excessive energy use
Narration : Waste is formed with distillation columns in the reboiler where excessive temperatures and unstable materials combine to form high molecular weight tars or polymers. Energy use leads to the direct release of criteria pollutants (CO, NOx, SOx, particle matter, volatile organic compounds) and global warming gases (primarily CO2)

27. Optimizing Use of Distillation Columns
Types of Seperation Technologies : Distillation Columns
Optimizing Use of Distillation Columns
The most common way to increase product purity in distillation are:
To increase the reflux ratio.
If a column is operating close to flooding (increasing reflux ratio is not an option), then adding a section to the column leads to higher-purity products.
There are several ways to decrease the generation of tars in the reboiler of the column:
Reducing the column pressure, resulting in lower reboiler temperatures.
Improving the process control technology = product purity specifications will be met
Narration : Increasing the reflux ratio for stable materials may be the easiest way to decrease waste generation due to inadequate product purity. To improve the process control technology (this will assure that product purity specifications will be met and reduce the possibility that off-spec product will be created)

28. Reactors and Seperators
Pollution Prevention for
Reactors and Seperators
REACTOR + SEPERATOR = REDUCTION OF BY- PRODUCTS
Examples:
Distillation:
Solvent recovery from waste water
Ink and solvent recycle
Batch distillation of used antifreeze
Solvent recovery and reuse in automobile paint operations
Narration : the combination of reactors and separators allows the reduction of byproduct generation from reactors and increases reactant conversion to products. These combinations of separators and reactors can involve either distinct units (continued on following page)

29. Extraction of a batch process residue
Pollution Prevention for Reactors and Seperators (cont)
Extraction:
Extraction of a batch process residue
Hydrocarbon recovery from refinery wastewater and sludge
Reverse Osmosis:
Closed-loop rinsewater for process electroplating
Recovery of homogeneous metal catalysis
Ultrafiltration:
Polymer recovery from wastewater

30. Pollution Prevention for Reactors and Seperators (cont)
Adsorption:
Natural gas dehydration
Replacement of azeotropic distillation (benzene, ciclohexane)
Membranes:
Recovery and recycle of high-value volatile organic compounds
Recovery of organic compounds fron wastewater streams
Metal ion recovery from aqueous waste streams

31. Pollution Prevention Applications for Separative Reactors
The separative reactor has a very high potential for reducing waste generation:
Hybrid systems that combine chemical reactions and product separation in a single process unit.
When chemical reaction and separation ocurr in concert, the requirements for downstream processing units are reduced, leading to lower capitals costs.
Unwanted byproduct generation can be minimized in series reactions by the removal of the desired product
Separation units that have been integrated with reaction include distillation, membrane separation, and adsoption.
Narration : An exciting new reactor type that has a very high potential for reducing waste generation is the separative reactor. These hybrid systems combine chemical reaction and product separation in a single process unit. When chemical reaction and separation ocurr in concert, the requirements for downstream processing units are reduced, leading to lower capitals costs. Unwanted byproduct generation can be minimized in series reactions by the removal of the desired product within the reaction zone and before significant secondary reactions can ocurr. Separation units that have been integrated with reaction include distillation, membrane separation, and adsoption.

32. Pollution Prevention Applications for Membrane Separative Reactiors
Reaction coupled with membrane separation also is used to increase the efficiency of chemical reactions:
Can be used to selectively remove either products or byproducts from the reaction zone
Overcoming low conversions in equilibrium-limited reactions and reduce waste generation in series reactions.
Can also be used to selectively permeate reactants into the reaction zone in order to control excessive byproduct formation (e.g. Permeation of O2 in partial oxidation or oxidative coupling reactions).
Narration : Much like adsorption-based separative reactors, the equivalent membrane-based unit can be used to selectively remove either products or byproducts from the reaction zone, thereby overcoming low conversions in equilibrium-limited reactions and reduce waste generation in series reactions. However, membrane-based separative reactors can also be used to selectively permeate reactants into the reaction zone in order to control excessive byproduct formation (e.g. Permeation of O2 in partial oxidation or oxidative coupling reactions).

33. Pollution Prevention Applications for Membrane Separative Reactiors
Additional challenges remain before commercial application of membrane separative reactors can be realized. These include:
Economical manufacture of thin, defect-free selective membrane layers over large surface areas
Leak-free reaction systems with high temperature seals
Elimination or reduction of sweep gases which dilute product streams
Enhanced membrane and catalyst performance, including resistance to foulding and deactivation

34. Storage Tanks and Fugitive Sources
Pollution Prevention for
Storage Tanks and Fugitive Sources
Storage Tanks
Fugitive Sources (valves, pumps, piping conectors, pressure relief valves, sampling conections, compressor seals, and open-ended lines)
Narration : Storage tanks are very common unit operations in several industrial sectors, including petroleum production and refining, petrochemical and chemical manufaturing, storage and transportation, and other industries that either use or produce organic liquid chemicals. Tanks are used for storage of fuels and for feedstock or final product buffer capacity. Fugitive sources are...
Other fugitive sources include :
Connectors: Numerous pieces are used to connect pipe to other pieces or to equipment and vessels.
And Seals : They’re commonly located around of leaks for fugitive sources such as valves, pumps, and compressors.

35. Pollution Prevention for
Storage Tanks
Storage tanks are very common unit operations in several industrial sectors:
Petroleum production and refining
Petrochemical and chemical manufaturing, storage and transportation
Other industries that either use or produce organic liquid chemicals.
Narration : Storage tanks are very common unit operations in several industrial sectors, including petroleum production and refining, petrochemical and chemical manufaturing, storage and transportation, and other industries that either use or produce organic liquid chemicals. Tanks are used for storage of fuels and for feedstock or finl product buffer capacity.

36. Pollution Prevention for
Storage Tanks
The main environmental impact of storage tanks:
Continual occurrence of air emissions of volatile organic compounds (VOC’s) from roof vents
Periodic removal of oily sludges from tank bottoms.
Tank bottoms are:
- Solids or sludges composed of rusts, soil particles, heavy feedstock constituents, and other dense materials that are likely to settle out of the liquid being stored.
Narration : The main environmental impact of storage tanks is the continual occurrence of air emissions of volatile organic compounds from roof vents and the periodci removal of oily sludges from tank bottoms. Tank bottoms are solids or sludges composed of rusts, soil particles, heavy feedstock constituents, and other dense materials that are likely to settle out of the liquid being stored.

37. Minimizing Pollution from Tank Bottom Sludges
Sludges from tank bottoms may be periodically removed and either treated via land aplication or disposed of as hazardous waste.
They may be prevented from settling to the tank bottom:
By the action of mixers that keep the solid particles suspended in the liquid.
The use of emulsifing agents that keep water and solids in solution and out of the tank bottoms.
Narration : They may be periodically removed and either treated via land aplication or disposed of as hazardous waste. As long as the bottoms components are compatible with downstream processes, they may be prevented from settling to the tank bottom by the action of mixers that keep the solid particles suspended in the liquid. Another method is to use emulsifing agents that keep water and solids in solution and out of the tank bottoms.

38. Minimizing Pollution from Storage Tank Air Emissions
Air emissions of VOC’s from storage tanks are mainly from petroleum and chemical processing facilities:
Working losses are the emission that stem from the normal operation of the chemical processing in response to the changes in liquid level within the tank
Standing losses are the emissions caused by the action of ambient changes in temperature and pressure
Narration : Air emissions of volatile organic compounds from storage tanks are a major source of airbone pollution from petroleum and chemical processing facilities:
Working losses are the emission stem from the normal operation of the chemical processing in response to the changes in liquid level within the tank
Standing losses are the emissions caused by the action of ambient changes in temperature and pressure

39. Minimizing Pollution from Storage Tank Air Emissions
The emissions from tanks are dependent on :
Vapor pressure of the stored liquids
Tank caracteristics (it´s type)
Paint color and condition (of the tank)
Geographic location of the tank
There are 6 major types of storage tanks:
Fixed roof
External floating roof
Internal floating roof
Domed external floating roof
Variable vapor space
Pressure tanks

40. Reducing Emissions from Fugitive Sources
Within individual components, leaks are localized near seals, valve packing and gaskets. These leaks are of two types:
Low-level leaks that may persist for long periods of time until detected
Sudden episodic failures resulting in a large release
Leaks can be prevented or repaired, and leakless technologies are available for situations where even small rates of release cannot be tolerated
Narration : Leaks may occur from connectors due to thermal deformation on correct assemblies or may result from cross-threading and incorrect assembly (of nut-and-ferrule types). For the fail of seals in valvles, there are two main types of “leakless” valves that have no emissions through the stem. They are bellows valves, which are expensive and are mostly used in the nuclear power industry, and diaphragm valves, in which a physical barrier (diaphragm) exists between the process fluid and the valve stem

41. Methods to Reduce Fugitive Emissions
There are two methods for reducing or preventing emissions and leaks from fugitive sources in the industry :
Leak detection and repair (LDAR) of leaking equipment
Equipment modification or replacement with emissionless technologies
Narration: Equipment modification to reduce fugitive emissions might involve redesigning a process so that it has fewer pieces of equipment and connections, replacing leaking equipment with new conventional equipment, or the inclusion of new emissions-reducing technology, and sealant injection.

42. Methods to Reduce Fugitive Emissions
LDAR Program
Equipment such as pumps and valves are monitored periodically using an organic vapor analyzer (OVA).
The wand of OVA is directed towards the suspected source of leakage on each piece of equipment ( i.e. at a packing nut on a valve, at a shaft seal on a pump.)
If the source registers an OVA reading over a threshold value, the quipment is said to be leaking and repair is required.
Narration: The nature of the repairs depends upon the piece of equipment and may require shut-down of the process, and would be conducted during regularly-scheduled shut-down times in order to minimize the number of upsets in process operation and reduce repair-related emissions.

43. Methods to Reduce Fugitive Emissions
The nature of the repairs varies :
It may involve something as simple as tightening a packing nut on a valve
It may require replacement of a seal on a pump or a gasket in a connector.
Industrial LDAR programs vary greatly:
Frecuency of monitoring and their effectiveness (monthly, quarterly, or annual basis using an OVA is the preferred approach)
Problems in detecting low concentrations of VOCs
Intensity of monitoring (area)
Costs of monitoring: establich the frecuency of monitoring
Narration : Guidance documents are available from the US EPA on detailed procedures to monitor for leaks and estimate for emissions for fugitive sources (US EPA 1993b). Constant monitoring of emissions using area monitors is possible when contaminants are detectable in very low concentrations. For cases where constant monitoring is either technically impossible or too expensive, periodic monitoring on a monthly, quarterly, or annual basis using an OVA is the preferred approach. Monitoring on a more frequent basis may be more costly, but has been shown to be more effective in reducing emissions.

44. Methods to Reduce Fugitive Emissions
Reducing fugitive emissions might involve:
Equipment modification (redesigning a process)
Considering fewer pieces of equipment and connections
Replacing leaking equipment with new conventional equipment.
Narration : Equipment modification to reduce fugitive emissions might involve redesigning a process so that it has fewer pieces of equipment and connections or replacing leaking equipment with new conventional equipment.