Removing hydrates for gas

The formation of hydrates in natural gas processing facilities and pipelines is a critical issue as hydrates can plug equipment, instruments, and restrict or interrupt flow in pipelines. Generally, hydrates will form when the temperature is below the hydrate formation temperature, normally with “free” water present, depending on the gas composition and pressure. 

In general, hydrates can be prevented by:-

1. Maintaining the system temperature above the hydrate formation temperature by using a heater and/or insulation or compression the gas.

2. Dehydration of the gas to prevent the condensation of a free water phase.

3. Injection of thermodynamic inhibitors to suppress the hydrate formation temperature in the free water phase. Methanol (MeOH) is widely used as an inhibitor in natural gas pipelines, particularly in cold climate facilities (e.g., Canadian environments). In these difficult environments, methanol injection is the most economical solution for preventing hydrate formation and is often the only option.The challenge

The determination of methanol injection rate can be a very challenging task for engineers -mainly because of methanol partitioning: the injected MeOH may partition into three phases: (a) the aqueous phase, (b) the vapor phase and (c) the hydrocarbon phase. \

Criteria:

GPSA: Folow the chapter

Aspen Hysys:

Do not use the Peng Robinson package 

This month (May 2015), Aspentech released HYSYS v8.8 with the addition of the Cubic-Plus-Association (CPA) fluid property package. The new CPA PP can more accurately model methanol phase behaviors, especially in the modelling of liquid-liquid equilibria (LLE) including the prediction of the partitioning of methanol between water and hydrocarbons in the hydrocarbon phase.

Albert'a climate change policy

The new policy is intended to urge consumers and companies to use lower-carbon, cleaner, and renewable energy resources instead of high-priced and high-emissions energy. The implementation of the policy will speed up the reduction trend in carbon emissions in the short term and in the longer term, it will create an environment encouraging innovative ideas and new technologies and make an opportunity for lower-carbon products to compete in the energy market 

At an initial price of $20 per tonne in 2017, rising to $30 in 2018, and rising at inflation plus 2 per cent after that, this is a tangible price on carbon that is within the range of reasonable estimates of the true cost of carbon. The new carbon taxation is evaluated to generate revenue of around $3 billion by 2018, and potentially increasing to over $5 billion by 2030 [1] 

Firms will pay a carbon tax of $30 per tonne, just like everyone else.
Facilities emitting 100,000 tonnes CO2E/yr or more from all sources are required to reduce their emissions per unit of production by 15% below their historical baseline emissions intensity in 2016 and to 20% in 2017. 
If a facility reduces its emissions intensity below its emissions target, it may generate “Emissions Performance Credits” (EPCs) [2] which can be banked and accumulated for future years or be traded in the carbon market. On the other hand, facilities with annual emissions intensity over the limit which are not able to improve their performance to meet their targets must acquire credits. They may either use their banked EPCs from previous years, or purchase EPCs from a different facility, or “Emissions Offset Credits”, or pay their carbon tax to the Climate Change and Emissions Management Fund.

Facilities that emit 100,000 tonnes of CO2 Annually

Under the existing SGER :

• Any facility that emits more than 100,000 tonnes of carbon dioxide (CO2) per year is considered a “regulated facility” and is required to reduce its emissions intensity by 12 per cent versus its operational baseline.
• Contribute to the Fund and purchase a Fund credit, the cost of which has remained at C$15/tonne of CO2 since July 1, 2007

After the Alberta's Climate Change policy

• Increasing the operational efficiency requirements from 12 per cent to 15 per cent to 20 per cent over two years will have a dramatic impact on existing facility operation.
• Increasing the costs of Fund credits from C$15/tonne to C$20/tonne to C$30/tonne will have a direct impact on a regulated facility’s compliance costs.

Aspen Hysys tricks

Finding if u fall in the supercritical region in Aspen Hysys

1) it will itself say that "A temperature stream is not found at requested condition" 
2) Press cntl + U to see the critical pressure and temperature
2) Look at the envelope curve

BUUBLE POINT / BOILING POINT / VP

setting vapour fraction = 0 or 0.00000001 gives u the vapour pressure at that temperature
It also gives u the bubble point since first bubble or boiling point  is formed at that point

DEW POINT

Alternatively setting vf = 0.99999999 or vf = 1 sets dews point 

VP and OP  VP > OP = Flashing 
VP = OP  = boiling 
VP < OP = Trying to boil

vapour pressure greater than operating pressure (for a multicomponent mixtures) just means that the liquid is flashing (Vapor-liquid mixture).



VP and Tmp. and Molecular weight
VP decreases with molecular weight and increases with temperature

PV  = NRT 
PV X Molecular Mass = mass RT 

Also for a a biggher moecular harder to break the bonds

• Hydrocarbon dewpoint calculations are very sensitive to trace amounts of heavier hydrocarbons. 
• The hydrocarbon dewpoint for an analysis which shows an amount of "C7+" can have a very different dewpoint depending on whether the heaviest component is assumed to be (e.g.) n-C7 or n-C10.
• One should be aware of the maximum pressure for the phase envelope (cricondenbar). In the supercritical (dense phase) region, the concept of a dewpoint is not applicable. However, it should be noted that HYSYS may apply a vapour fraction of 0 or 1 in the supercritical region as an indication of which correlations are being used for the stream.

H20 demand in oil and gas industry

 Water demand is extensive in non conventional oil and gas extraction namely, SAGD, mining, and  hydraulic fracturing.

Water and energy demand are interlinked. Increasing the efficiency of one effects the other.


Produced water treatment operations, required to protect the environment and recycle more water, increase the cost and the energy requirements to extract these resources.
Evaporator, WLS, and ZLD technologie sin SAGD.

Directive - 081 state that SAGD CPF technology need ts to recycle

3 % - fresh water
30%  - brackish water
10% - produced water

Overcoming solution is reusing municipal wastewater by industry have started to become interesting for some facilities.

Water sourcing selection criteria include environmental impact, stakeholder relations, availability, timing, quality and economics. 

A particular technical challenge that may limit the use of some water sources is that of "compatibility" with reservoir characteristics- scaling could become a major problem if ignored. 

Aspen Hysys and Aspen Plus and Pro

ASPEN PLUS

• ·      Aspen Plus Has Solids Handling Capabilities In It.
• ·      It Has An "Automatic Recycle" Capability Whereas In HYSYS You Have To Add Them Manually.
• ·      Better User Interface
• ·      Good For Polymers
• ·      Aspen Plus Evolved As A Chemical Process Simulator - It Is Very Strong For Simulating Non-Ideal Properties, Systems With Electrolytes, Solids, Azeotropes, And Chemical Reactions. It Is Also Strong For Modeling Large-Scale Flowsheets (Using The Equation-Oriented Approach).
• ·      Aspen Plus Thermodynamic Library Is Considered To Be Quite Extensive And Hence Considered Quite Useful In Simulation Of Fine Chemicals And Pharmaceutical Chemicals
• ·      Aspen Plus Is Better Suited For Chemical Process Design Whilst HYSYS Is Best For Hydrocarbon Process Design (Both Upstream And Downstream But Mainly Downstream). 
• ·      Very Absurd And Obsolete Dynamic Module.

PRO II

• ·      Bad Support
• ·      Much More Friendly - Easy To Set Up
• ·      Runs Many More Iteration With Just One Click As Compared To Hyssops
• ·      We Can Model Solids Inside It 
• ·      We Can Develop An Entire Spreadsheet On The Flowsheet To Perform Sensitivity Analysis And See The Result At Once
• ·      However We Have To Create A Spreadsheet For It For Specific Label On The Flowsheet
• ·      We Can Ignore A Specific Section Of  Flowsheet And Conserve The Rest And Then Converge The Remaining
• ·      Suplur Removal Unit Can Set Up A Unit Operator With Specifications At The Outlet
• ·      Crashes a lot more

HYSYS

• ·      Hard To Set Up
• ·      Good Support
• ·      Hysys Cannot Model Sulfur Recovery Units, Either. However, Hysys May Be Able To Do Some Processes Outside Of Oil & Gas, I Don't Know, Never Tried.
• ·      Hysys Cannot Model Any Sour Process Or Wet Process Very Well.
•  

PROMAX

• ·      Amine Sweetening, Dehydration And Sulfur Recovery Makes Promax The Best

Flarenet avoid an excessive back pressure scenario

Excessive backpressure at a pressure relief valve may affect the performance of that valve, potentially resulting in instability and/or significantly reduced flow capacity, jeopardizing the safety of the equipment which the valve is meant to protect. The following discussion addresses how excessive backpressure can be addressed using Flarenet.
We can avoid a back pressure scenario by:

- Increasing pipe size
- Changing PSV type (balanced bellow instead of conventional)
- Introducing jump overs
- moving the load to another section of the flare

Flarenet and hysys

Flarenet

- Specially good for high velocity and low diameter pipes
- Good for complex network as found in refineries especially Good for loop system where direction of flow is not known in advance
- Good for earlier design when the pipe sizes r not confirmed.. since flarenet calculates the entire network for all scenarios
- Drawback : Make sure flarenet converse to a tolerance of 1 e -2
- Flarenet provides the ability to do design calculations, meaning that the required header and lateral sizes for the flare network are calculated, ensuring that system constraints such as valve backpressure and velocities are not exceeded.

psv inlet and outlet critera

INLET
Pressure drop less than 3 %

OUTLET
less than 0.7 MachPressure drop is less than 10, 50, 90%

momentum criteria pv2<200,000 pa

Effect of Temperature and Pressure of Density and Viscosity

DENSITY

LIQUID

TEMP. - As temp increases as density decreases (Inversely) 

For example at low temp. the bitumen is thick, more dense. As temp. increases, the density of bitumen is lower.

PRESSURE - As pressure increases as density increases (Directly) 

At the core of earth when the pressure is the high, the core liquids is thick, more dense.

GASES

TEMP. - As temp increases the density decreases (Indirectly) 

The gas at the surface of heath gets hotter and its moves up, less dense. Cold gases come down on the earth.

PRESSURE - As pressure increases the density increases (Directly) 

For example at low pressures  the gas are moving at lower speeds, low inter-molecular forces. As temp. increases, the gas molecules more around faster, more dense. 

PV =nRT

VISCOSITY

While liquids get runnier as they get hotter, gases get thicker. (If one can imagine a "thick" gas.) 

LIQUID

TEMP. - As temp increases the viscosity decreases (Inversely) 

Honey and syrups can be made to flow more readily when heated. Engine oil and hydraulic fluids thicken appreciably on cold days and significantly affect the performance of cars and other machinery during the winter months. the viscosity of a simple liquid decreases with increasing temperature (and vice versa). As temperature increases, the average speed of the molecules in a liquid increases and the amount of time they spend "in contact" with their nearest neighbors decreases. Thus, as temperature increases, the average intermolecular forces decrease. 

PRESSURE - At very high pressures, as pressure increases the viscosity increases (Directly) 

Viscosity is normally independent of pressure, but liquids under extreme pressure often experience an increase in viscosity. Since liquids are normally incompressible, an increase in pressure doesn't really bring the molecules significantly closer together.

GASES

TEMP. - As temp increases the viscosity increases (Directly) 

The viscosity of gases increases as temperature increases and is approximately proportional to the square root of temperature. This is due to the increase in the frequency of intermolecular collisions at higher temperatures. Since most of the time the molecules in a gas are flying freely through the void, anything that increases the number of times one molecule is in contact with another will decrease the ability of the molecules as a whole to engage in the coordinated movement. The more these molecules collide with one another, the more disorganized their motion becomes. 

PRESSURE - Independent

The viscosity of an ideal gas is independent of pressure, and this is almost true for real gases. In gases, Viscosity arises mainly because of the transfer and exchange of molecular momentum. How come pressure doesn't affect the viscosity then?

Double the pressure, and you double the number of molecules arriving at a surface, but on average they will only have come from half as far away, and the effects cancel out

Density, Specific weight /volume/gravity

DENSITY (Kg/m^3  or N•sec²/m^4)

Density is defined as mass per unit volume. Mass is a property.

Density can be expressed as

ρ = m / V

SPECIFIC VOLUME (m^3/kg  or m^4/ N•sec²)

Specific volume on the other hand is the reciprocal of density.

Specific volume  = 1/ density

SPECIFIC WEIGHT (N/m³ or lb/ft³ or kg/m²•sec²)

Specific Weight is defined as weight per unit volume. Weight is a force.

γ = ρ g        

SPECIFIC GRAVITY /RELATIVE DENSITY (Dimensionless)

For liquids defined as the ratio of the density of a substance to the density of water - at a specified temperature.

SG = ρ_substance / ρ_H2O 

The reference density of water at 4^oC (39^oF) is used as the reference as these are the conditions of maximum density.

For gases

SG = Mass of gas / Mass of air = Mass of gas / 28.97