CHBE 403 Unit 1

what is design?

human-centered approach to innovation that draws from designer’s toolkit to integrate needs of ppl, possibiliites or tech, and requirements for business success

what types of design constraints are there?

chemical, thermodynamic, mechanical, economic, legal, standards/codes, ethical, social (work outside in)

what are steps of design process

1) identify client needs

2) identify constraints

3) agree w clients on what success consists of

4) think thru possible options

5) identify what data u need and collect said data

6) pick leading contender

7) design, build, and test lead options

8) iterate and improve

9) document results

what are the different FEED stages?

feed = front-end engineering and design

1) FEL 1 (front end loading): conceptual phase

2) FEL 2 = feasibility phase

3) FEL 3 = definition phase

• do final investment decision (FID) after FEL3

4) EPC

5) operate

what are the components of plant?

what does battery limits mean?

battery limit = a physical or virtual boundary that defines the scope of work, liability, and transfer of responsibility between different parties or process units in an industrial plant

things u have to consider inside/OH:

• the pipe from the storage tank to the unit?

• the electrical substation?

• the cooling-water system?

• the product transfer piping?

• The wastewater treatment?

what is normally outside battery limits? what’s another name for this

aka offsites

Includes: Utility generation (steam, cooling water, power), storage tank farms, flare systems, product loading docks, interconnecting pipe racks, and administrative buildings.

what is normally inside battery limits? what’s another name for this

onsites

Includes: Reactors, distillation columns, heaters, pumps, compressors, and specific equipment directly tied to the primary production process

define supply chain + draw what it looks like in chem industry

what are mcglam pet peeves on BFD/PFDs

• label streams / describe contents in stream table

• 
  

what r things u need to triple check on synthesis questions

• only use flash drum for super easy separations (H2/methane from other materials) - for all else u have to use tower

• recycle H2 anytime you can + u have to compress recycle hydrogen

• good to have a heat exchanger before reactors (don’t necessarily need on recycle stream)

• typically have condenser before distillation bc if u feed pure vapor to distillation tower it all just goes out the top

• use a furnace when dealing with T>350C (600F) superheated steam max temp is ~350C so u can only use HX to that high

• should write CW on condensers/coolers (or just label whatever the utility is)

• should have urge stream for all h2 recycle

• label every piece of equip

• remember u may need reboiler and condenser unless told otherwise

• generally mix into one inlet stream and input instead of multiple inlets

what is point of piping isometric diagram

shows you lengths/heights of pipe runs

what does mcglam call GAs

plot plans

what does PAR stand for

predict, authenticate/analyze, re-evaluate/re-think

define coproduct

“item for sale that is not the basis for the plant’s capacity”

market or customer (internal or external) exists for coproduct

usually sold or transferred internally

USEFUL de

define byproduct

not useful

any material w/out significant market or customer

usually disposed as waste or used as substitution for fuel

can sell, but u can’t rlly ctrl how much you sell it for - no one rlly wants it so the buyer tells you how much they’ll pay for it

what are key steps for process synthesis

• decide batch/cts

• determine input/output structure

• determine recycle process

• figure out separation

  • optimize energy structure

why is batch favorable?

• good @ low volume

• need accountability and track where stuff comes from

• if ur making different versions or formulas and need to switch between them [flexible use of equipment]

  • good for seasonal stuff

• easier to deal w if it breaks down bc u can take down that part without ruining entire process [“tolerance for processing inefficiency”]

• good for slow rxn rates bc don’t have to use a rlly long large container to have enuf time - just let it sit in same place for a while

• better @ dealing w fouling

  • just clean in between batches instead of having to do massive shutdown and cause issues elsewhere

what are 3 reasons u would want to remove a feed impurity

1) it’s reactive and there’s a lot of it (might consume reactant that u need for main rxn and makes unwanted byproduct instead, reduces yield)

2) is catalyst poison or creates catalyst poison (catalyst super expensive)

3) inert + there’s a lot of it ($$ infrastructure)

when is it fine to leave feed impurities in feed?

1) it’s inert + easier to separate from product than feed

2) inert + in a gas feed (gas separations are $$)

3) in liquid feed + part of product/byproduct (helps u make $)

4) azeotrope w reactant (more work than it’s worth to separate)

what are all the options for type of product streams

1) primary prod

2) coprod

3) byprod

4) recycle and purge

5) recycle to extinction

6) fuel gas

7) fuel liquid

8) liquid waste

9) solid waste

10) gaseous waste

11) vent

what are you allowed to vent

Nitrogen, oxygen, CO2 (eh), water, argon [anything in air]

what compounds do u normally send to fuel gas

H2, CO, methane, ethane, propane (light hydrocarbons) [sometimes butanes and ehtylene/propylene]

what is the general guideline for weight of materials u recycle as vapor

stuff lighter than propylene

if heavier than propylene u should condense and recycle as liquid (able to condense bc Tc_prop > T_ctw so CTW is sufficient to condense it)

what attributes r u looking for in excess reactant (if A+B —> C)

1) if B is rlly hazardous and u need to get rid of it then make A the excess to u def get rid of B

2) add a ton of A if reactant B might also react with C and BC is undesirable

3) add a lot of A if B is hard to separate from C so u def only have C and don’t have to separate B from C

4) add a lot of A if it has to diffuse, increasing partial pressure will make diffusion better

5) add a lot of A if you might have coking - helps fill the pores

6) fine to add a ton of A if it’s benign and safety lreleased (like if u feed in a bunch of O2 that’s fine bc can just leave in vent)

7) favor liquids bc easier to recycle [compressors $$]

8) or just don’t have excess if u don’t need it

how can u adjust equilibrium conversion?

1) adjust pressure

2) use diluet gas

3) remove ur product quickly so ur always pushing forward in effort to balance

4) remove coproduct (same rationale as above)

what are penalities for keeping inert in feed

• Increased equipment size

• Need for separation to remove the inert

  • Decreased equilibrium conversion and/or reaction rate

what are some general rules for recycle streams

1) u wanna recycle unreacted feed to save $ esp if feedstock is $ - pricier feed justifies less purge and more recycle

2) recycle as close to rxn as possible

3) must recycle gas and liquid sep bc pump only work for liq and compress only work for vap

4) gas only lighter than propylene

5) pumps cheaper than compressor so pump when u can

6) consolidate like-phases whenever possible

do u want product in top or bottom and why

want in top bc bottom = liq so it fouls a lot and introduce contaminants

what are bounds for temp and pressure for target operating conditions

40C < T < 400C

_> 40C bc CTW at 30C so if u want to be able to cool u need hotter than CTW

> 400C bc starts screwing w tensile strength above carbon steel and other materials

1 bara < P < 10 bara = 14.5 psia < P < 145 psia

whats typical P and T of HPS

40-50 barg, 250-265C (but u can get up to 100barg steam @ 310C heating)

why would you make exceptions to upper T design limit and what does that impact

why:

favor equilibrium for endothermic, increase rxn rate, improve selectrivity, keep gas phase

what impact:

pay for furnace and need special MOC

why would you make exceptions to lower T design limit for reactors and what does that impact

why:

good for exo rxn + considerate of temp-sensitive materials (heyo bio) + improved selectivity + can keep stuff in liq phase

impact:

refrigeration is $ + special MOC

why would you make exceptions to lower T design limit for separators and what does that impact

why:

condensing is a V/L separation options, u can crystallize at low T

impact:

$ refridg and special MOC

why would you make exceptions to upper P design limit for reactors and what does that impact

why:

help w equil conversion, increase rxn rate, lets u keep liquid phase

impact:

thicker walls and pricier to fabricae

what are cons of going below design P lower limit

• need larger equip bc larger vol at low P

  • can have air leaks which are dangerous

at what pressure ratio do u worry about ur compressors? what r consequences and how do u mitigate

P_out/P_in > 3

requires high shaft work, seal damage from high outlet temp, lubricant decomposes

soln:

break into multiple compressor stages

what are common places to see exergy losses?

deltaT_logmean > 100C on HX

P_out/P_in > 3 for compressors

high inlet T on compressors

big deltaP across valve

mixing streams w big diff in T and P

what is the only sep tech that can have high recovery and high purity

distillation

like if u input A and B u can get a distillate that’s 99.9% A and contains ~ 99% of the A you had in the feed (not lose A along the way)

• unlike membrane where u can recover a lot of A (get most of it thru the membrane) but if u do that it’s less pure bc less stringent membrane will also allow other stuff thru

when use gas adsorption / strip

absorb low concen species from gas into liq

strip low concen from liq into gas

when use LLE

if have close BP but are chem dissimilar

sep ionic from nonionic

sep temp-sensitive materials

when use membranes

purify liq from solutions contains salt or high MW organics

separate light gas from heavy gas based on diffusion rate

when use crystallization

separate two solids or precipitate solid from liqwhat

what is leaching sep. tech

remove solid from solid mixture by dissolution in a liquid

what does MSA stand for

mass separating agent

these are annoying bc u have to recycle and regenerate them and have to have some makeup stream bc some will get lost in purge

how do you determine what you want to remove first in a series of separation steps

1) REMOVE NONCONDENSABLE GASES

2) remove hazardous or corrosive materials

3) remove large product stream

4) remove stuff w high heat of vap (reduces future reboiler duties)

5) do easiest separation steps first so when u get to the pt of doing hard sep steps ur working w lower volumes

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want products in the top

what are algorithm options in process sim

1) sequential modular (solve each unit op 1 @ a time and keep iterating - most popular)

2) simultaneous modular (solve whole thing @ 1x with a big set of nonlinear eqn, hard to set up but converges easily)

3) simultaneous nonmodular (dont worry ab this one)

what info do u have to specify if ur working w component not in database

1) vapor pressure + liquid density

2) critical T & P

3) use ridel eqn and corresponding states

when do you use EOS instead of activity coefficient models? what are common EOS

• good for gas or supercritical

• good for hydrocarbon

• NOT good for polar

common:

• SRK and Peng Robinson

what is design spec? how is it different than parameter?

defn spec: “performance metric to be achieved by a unit operation”

defn param: “attributes of a unit operation THAT CAN BE CHANGED to meet design spec”

ex: to hit spec of 53% outlet mole frac ethylene, ur design parameter to hit that would be 5 column trays

what’s an example of a design parameter?

feed composition, # trays, HX SA

what are the usual parameters for adiabatic flash / what are typical specs

params:

feed flow rate

feed composition

specs:

T&P

overhead and bottoms flow

what specifications does mcglam recommend using on V/L separations

a) overhead flow rate and reflux ratio

b) reflux rate and boil-up rate

above are better than:

overhead flow rate + purify

overhead and bottoms flow rates

formula for single-pass conversion

formula for overall conversion

defn product selectivity

defn product yield

defn component purity

defn component recovery

what’s the difference between design and rating

design = equip doesn’t exist —> given xyz design specs, what parameters wil meet them

rating = equip does exist and ur adjusting —> given xys design parameters, what specs can u hit? [given reactor vol, what is outlet concentration]

what organization has commonly used boiler and pressure vessel codes

ASME (american society of mechanical engr)

what is the minimum threshold for ASME pressure vessel codes to apply to

must be at least 15 psig (1 bar)

what symbol is important on ASME code stamp name plates

U

tells u that the vessel has been designed, inspected, and certified by ASME certified individual (like PE signoff)

is design pressure higher or lower than max operating pressure

higher - u do all DESIGN calcs and material decisions based on DESIGN pressure, which has to be able to withstand max operating pressure

how do you determine design pressure?

design pressure = 1.1 x max operating pressure (psia)

OR

design pressure = max operating pressure + 0.33 bar [5psi]

^^ whichever one gives larger design P

what is the minimum design pressure

1 barg or 15 psig (including hydrostatic head)

ASME VIII only covers stuff above this pressure and it’s good to show ur stuff is certified, so want to be able this minimum

what is MAWP

max allowable working pressure = rating of the materials / vessel you’re using

changes w time bc stuff wears down

how does MAWP compare to design pressure

MAWP >= design P > max operating P > normal operating P

bc MAWP is a function of the vessel and may only come in standard thicknesses. these must have limits that exceed design P

ex: code calculation might say you need a 0.41 inch wall, but plate comes in standard thicknesses, so you buy 7/16 inch

do pressure relief settings change with time? what do they depend on?

yes, changes with MAWP

what is design P for vessels operating at vacuum?

1 barg / 15 psig AND full vacuum

what are possible sources of vacuum

vacuum operation

autorefrigeration during pressure relief that causes condensation

pumping out liquid w/out good vent

in hx, is shell or tube higher P

tube (easier to design smaller tubes to withstand high P than making entire shell suitable for high P)

what are design specs for pressure rating shell of shell/tube HX

a) put rupture disk on shell

b) shell design pressure = (10/13) tube prssure

c) hydrotesting is done at 1.3x shell design pressure (ensures it can def handle what’s thrown @ it)

what is relationship between design T and max operating T

design T = 25C/50F + max operating T wha

what is CET

lowerst temp which vessel will be subjected to ocnsidering

• lowest operating temp

• operational upset

• autorefrig upon depressure

  • lowest atmospheric temp

what is MDMT

minimum design metal temp

must be lower than CET bc should be able to handle all worst case scenarios

similar idea to MAWP where this is a rating of the equipment

how do u calculate distillation tower vapor velocity and diameter

@ 80% flood

how do u determine pump or pipe capacity

= 110% of basis stream-day rate

how compute tensile strength

= 300% of that @ design P

how air dew point impact cooling tower design

cooling tower design based on 90%tile air dew point

what is typical aspect ratio of cylindrical vessels?

2-4:1 height:diameter

when are horizontal vessels useful?

• good for phase sep that require low velocity for settling

  • easier to clean internals

what vessel head shape is best at high T

hemispherical

what P range is ellipsoidal vessel head good for

P>15barg

what P do you use torispherical for

cheapest for P<15barg

is flat or hemispheirical head thicker

flat

what is tangent line

where curve begins

what type of support do u use on tall vessels

skirt (not beam or leg)

what is the main application of ceramics

used in high T high corrosition

used in reactor and furnace @ low P , can also use for gasket and seal

what’s diff btween thermoplastic and thermoset

plastic softens as T increase, set hardens as T increase

what are most common thermoplastic resins

PVC or HDPE

when do you use thermoplastics and thermosets

used for low T low P piping and storage vessels

most common thermoset resins

GRP

glass reinforced polymer

what do u use elastomers for

gaskets, seals, tank liningss, pneumatic hoses

what are the most common metals

carbon steel + 304SS + 316SS

what utilities are outside of process design

electrical gen

fuel gas dist

plant/intrument air

fire supression

safety flare

defn wet bulb temp

Wet bulb temperature is the lowest temperature that air can cool itself down to purely through the evaporation of water into it.

formula for cooling water approach

T_CW - T_WB (want CW > WB bc WB needs to be able to remove heat from water)

what is minimum cooling W approach temp

5F (but usually closer to 15F) =15C

approach temp directly impact tower size

formula for cooling tower range + what’s typical value

T_hw = T_cw = T(water entering cooling tower) - T(water leaving coolng tower once heat is removed)

usually 5-20F, assume 10F