process operability class materials process efficiency copyright © thomas marlin 2013 the copyright...

Process Operability Class MaterialsProcess Efficiency

Copyright © Thomas Marlin 2013The copyright holder provides a royalty-free license for use of this material at non-profit

educational institutions

FC1

LC1

FC

1

TC

1

TC

2

T

10

T

12

T

11

T

13

fuel

LC

1

L2

LAHLAL

F

4

Basic flowsheet Design with Operability

PROCESS OPERABILITY: EFFICIENCYKey Operability

issues

1. Operating window

2. Flexibility/ controllability

3. Reliability

4. Safety & equipment protection

5. Efficiency & profitability

6. Operation during transitions

7. Dynamic Performance

8. Monitoring & diagnosis

In this Lesson, we will learn

• The objective and degrees of freedom

• Improvement through equipment selection

- Pump/fluid flow

• Improvement through equipment utilization

- Pump/driver, boiler

• Improvement through process structure

- Ethylene plant, packed bed chemical reactor

• Improvement through operating conditions

- Fired heater/reactor, Flash, CSTR

EFFICIENCY

Efficiency: We will use this term to imply good economic performance, which can result from improved product quality, increased product rate, lower raw material, effluent and energy consumption, or other improvements.

Others might say “optimization”.

• Increase: profit = sales – feed – fuel – electricity - …

• Reduce effluents (e.g., total SO2, particulates, etc.)

• Reduce greenhouse gases

• Reduce use of feed (natural resources)

Degrees of freedomKey Operability

issues

1. Operating window


3. Reliability






EFFICIENCY

1. Safety

2. Environmental Protection

3. Equipment protection

4. Smooth operation production rate

5. Product quality

6. High profit


Let’s recall that these objectives have higher priority. They must be achieved; then, we seek to increase profit.

Objectives 1-5

Profit/Efficiency

Additional flexibility is required for increased efficiency & optimization

Degrees of freedomKey Operability

issues

1. Operating window


3. Reliability






EFFICIENCY

Approach 1: Design with the appropriate equipment capacities.

Recall the general tradeoffs in sizing process equipment.

Advantages

Disadvantages

Small equipment

Large equipment I can complete

and check with answers in Operating

Window topic.

Not too big

Not too small

Just right!

Equipment capacitiesKey Operability

issues

1. Operating window


3. Reliability






EFFICIENCY

Efficiency through equipment capacity: Equipment with excessive capacity can operate at lower efficiencies.

Let’s purchase a really large centrifugal pump for this application. What do you recommend?

Constant speed centrifugal pump


issues

1. Operating window


3. Reliability






EFFICIENCY

Efficiency through equipment capacity:

Flow rate

head

Pump head curve

“system” curve, pressure drop vs flow rate

Steady-state flow rate at given conditions



issues

1. Operating window


3. Reliability






EFFICIENCY


Flow rate

head

To achieve the desired flow, we compensate for the larger pump by causing a large pressure drop across a valve .

Too large a pump wastes energy.

Do not oversize pumps!



issues

1. Operating window


3. Reliability






EFFICIENCY


Flow rate

head

Most likely flow rate The constant speed

centrifugal pump (red curve) is selected to

• Provide sufficient flow for the maximum demand

• Operate near its maximum efficiency at the most likely (design) flow rate

The control valve affects the system (blue) curve

• Usually about 70% open at design (but, must provide maximum flow rate)


issues

1. Operating window


3. Reliability






Follow-up Point #1 - Efficiency through equipment capacity:

EFFICIENCY


Do we always install a controlvalve? If not, why?


issues

1. Operating window


3. Reliability






EFFICIENCY


Flow rate

head

No control valve resistance

The constant speed centrifugal pump (red curve)

The flow is the maximum for the system, pump and piping design.

When the optimum flow rate is always the maximum flow, we do not use a control valve.

Example, cooling water utility in a chemical plant.


issues

1. Operating window


3. Reliability







EFFICIENCY


Do we always install a constant speed pump? If not, why?


issues

1. Operating window


3. Reliability






EFFICIENCY

Follow-up Point #2 - Efficiency through equipment capacity: More flexible equipment can save energy at the expense of higher capital costs.

An alternate design uses a variable speed source of power (motor or turbine). (The control valve is not needed.)

This design is more energy efficient and may be the best economically (e.g., lowest NPV).


issues

1. Operating window


3. Reliability







EFFICIENCY


What is the best pipe diameter?(Best = trade-off of capital and

operating costs)


issues

1. Operating window


3. Reliability






EFFICIENCY

Follow-up Point #3 - Efficiency through equipment capacity: A larger pipe diameter reduces pump work but increases piping costs.

Pipe diameter “rules of thumb” (guidelines, Woods, 1995)

• Pumped liquid - velocity of

• Vapor - velocity of

See Woods (1995) for correlations for many systems and fluids


issues

1. Operating window


3. Reliability






1 m/s

20-30 m/s

EFFICIENCY

Approach 2: Use existing equipment in most efficient manner.

We provide extra equipment to

• Increase reliability

• Expand the operating window

• Increase flexibility

• To capitalize on optimization opportunities

Equipment utilizationKey Operability

issues

1. Operating window


3. Reliability






EFFICIENCY

Efficiency through equipment utilization: We can use the lowest cost from parallel equipment.

motor

steam

Depending on the time of day and the steam usage elsewhere in the plant, the lowest cost source of work can change! We have the flexibility to respond.

Decision is usually made and implemented by a plant operator

electricity

turbinePumps with different power sources


issues

1. Operating window


3. Reliability






EFFICIENCYEfficiency through equipment utilization: The total demand of steam must be satisfied. The steam can be produced in boilers with different efficiencies. We can optimize.

PC

PYx

PYx

PYx

PYx

We adjust the ratios to lower fuel cost; fast pressure control not affected.


issues

1. Operating window


3. Reliability






EFFICIENCYEfficiency through equipment utilization: Several boilers provide increased reliability. Also, they allow boilers to be operated near their maximum efficiencies, compared with one large boiler, as the total steam demand changes.

80.00

81.00

82.00

83.00

84.00

85.00

86.00

87.00

88.00

efficiency

0.00 0.20 0.40 0.60 0.80 1.00 steam production

boiler 1

boiler 2

boiler 3

boiler 4


issues

1. Operating window


3. Reliability






EFFICIENCY

Efficiency through equipment utilization

We must satisfy the plant demand. How much steam from each boiler (i = 1,4)?

Minimize total fuel = (fuel)i

when

(Steam)i = Demand

(fuel)i = (Steami*Hvap)/(Hcombust * i)

i = f(Steami)

We will learn how to formulate and solve this type of problem in 4G03.


issues

1. Operating window


3. Reliability






EFFICIENCY

Approach 3: We can increase efficiency by designing the best process structure (synthesis).

We provide extra equipment to

• Recover & recycle unconverted feed

• Recover & recycle solvent

• Recover & reuse effluents (e.g., water)

• Use heating (cooling) far from ambient

• Thorough economic analysis is required to find the best investment of capital and operating costs

Equipment synthesisKey Operability

issues

1. Operating window


3. Reliability






0

0

0

RXN

FRACT

COMP

REFRIG

DIST

Ethane feed

Pro

duct

s: H

ydro

gen

to g

asol

ineNaphtha

feed

EFFICIENCY

Propose a process structure change to increase efficiency/profit

Equipment synthesis

ethane

ethylene

propylene

butadiene……..

naphtha

Hydrogen,

methane

0

0

0

RXN

FRACT

COMP

REFRIG

DIST

Ethane feed

Pro

duct

s: H

ydro

gen

to g

asol

ineNaphtha

feed

EFFICIENCYPropose a process structure change to increase efficiency/profit

Equipment synthesis

ethane

ethylene

propylene

butadiene……..

naphtha

Hydrogen,

methane

Recycle unconverted ethane to reactors

EFFICIENCY

Efficiency through process structure:.

Discuss this packed bed reactor with an exothermic reaction.

Is this the best design? What alternative(s) would you evaluate?

FC

1

CW

Steam

Cold feed

Hot effluent


issues

1. Operating window


3. Reliability






heat

cool

FC1

EFFICIENCY

Efficiency through process structure: We want to use raw materials and “energy” (material significantly hotter or colder than ambient). One typical structure involves recycle.

Discuss this packed bed reactor with an exothermic reaction.

• Advantages

• Disadvantages

The reactor effluent is hot.

Cold feed

Hot effluent

Cold product


issues

1. Operating window


3. Reliability






EFFICIENCY

Efficiency through process structure: One typical structure involves recycle. FC

1

Advantages

Disadvantages?


issues

1. Operating window


3. Reliability






EFFICIENCY

Efficiency through process structure: One typical structure involves recycle. FC

1

Advantages

• Good energy efficiency(exhaust to environment closer to ambient)

• Cannot startup the process (need heating)

• No flexibility for changing operation

• Poor dynamics (see section of dynamic performance)

I suspect thatwe are notthrough withthis exercise!

Disadvantages?


issues

1. Operating window


3. Reliability






EFFICIENCY

Approach 4: We can increase efficiency by selecting the best values of operating conditions.

Many conditions can be changed in the process that do not affect safety …. product quality, but they affect profit, e.g.,

• Recycle compositions• Conversion in a chemical reactor• Intermediate separation

• The best values can change from day to day

• Thorough economic analysis is required to find the best (optimum) conditions

Operating ConditionsKey Operability

issues

1. Operating window


3. Reliability






EFFICIENCY

Goal: Maximize conversion of feed ethane but do not exceed 864C

What is the best value of the reactor temperature?


issues

1. Operating window


3. Reliability






EFFICIENCY

Goal: Maximize conversion of feed ethane but do not exceed 864C

“Constraint Control” to push against the constraint: Operate as close to 864 as is possible, given typical variability


issues

1. Operating window


3. Reliability






Feed

Vaporproduct

LiquidproductProcess

fluidSteam

F1

F2 F3

T1 T2

T3

T5

T4

T6 P1

L1

AC

L. Key

EFFICIENCYEfficiency through operating conditions: In many conditions, product can be made efficiently or inefficiently by changing process variable values within the operating window.

How do I decrease energycost?


issues

1. Operating window


3. Reliability






Feed

Vaporproduct

LiquidproductProcess

fluidSteam

F1

F2 F3

T1 T2

T3

T5

T4

T6 P1

L1

AC

L. Key

Use the least costly heating

EFFICIENCYEfficiency through operating conditions: In many conditions, product can be made efficiently or inefficiently by changes process variable values within the operating window.


issues

1. Operating window


3. Reliability






EFFICIENCY

R e f o r m a t e

L S R N a p h t h a

N - B u t a n e

F C C G a s

A l k y l a t e

F i n a l B l e n dF T

A T

F C

F C

F C

F C

F C

F l o w s e t p o i n t s

T A B L E O F C O M P O N E N T D A T A

f l o w v a l u e O c t a n e R V P V o l F l o w m a x F l o w m i n C o s t( O c t . n o . ) ( p s i ) ( % ) ( B l / d a y ) ( B l / d a y ) ( $ / B L )

R e f o r m a t e 5 4 2 4 . 5 3 1 9 9 1 . 8 4 1 7 6 0 0 0 0 3 3L S R - N a p t h a 7 9 2 . 9 5 8 1 3 6 4 . 5 1 2 8 5 8 5 0 0 2 7n - B u t a n e 2 8 2 . 5 0 9 9 6 9 2 . 5 1 3 8 1 1 5 3 5 0 2 5 0 1 2F C C G a s o l i n e 0 7 8 6 2 2 3 0 0 0 0 3 2A l k y l a t e 0 9 6 . 5 7 3 0 3 0 0 0 0 3 8 . 5

T A B L E O F P R O D U C T D A T A

f l o w O c t . m i n O c t M a x R V P m i n R V P m a x V o l m i n V o l m a x F l o w m a x F l o w m i n v a l u e( B l / d a y ) ( O c t . n o . ) ( p s i ) ( % ) ( B l / d a y ) ( $ / B l )

R e g u l a r p r o d u c t 6 5 0 0 8 8 . 5 1 0 0 4 . 5 1 0 . 8 0 3 0 6 5 0 0 6 5 0 0 3 3 . 5

Efficiency through operating conditions: In many conditions, product can be made efficiently or inefficiently by changing process variable values within the operating window.

Blend these components

To meet product specifications


issues

1. Operating window


3. Reliability






EFFICIENCY

hydrogen

gas

reformate

feed

Efficiency through operating conditions: In many conditions, product can be made efficiently or inefficiently by changing process variable values within the operating window.

How much H2 recycle?

Best reactor

T

Best Feed

flow rate


issues

1. Operating window


3. Reliability






PLANT, SENSORS, REGULATORY CONTROL

Data Evaluation

Model UpdatingModel

Optimizer

Results analysis

Advanced control

Model parameters

measurements

plant operations

EFFICIENCY

Efficiency calculations can be automated when conditions change frequently.

This is basically

HYSIS run many times to obtain the

optimum answer*

* Solution approaches covered in 4G03

Model predictive

control


issues

1. Operating window


3. Reliability






SUNOCO OPTIMIZER RELIABLY SOLVES LARGE SYSTEMS AND EARNS SUBSTANTIAL BENEFITS

Smithsonian Award-winning application in Sarnia by SUNCOR

Operating Conditions

EFFICIENCY

INDUSTRIAL PRACTICE

• Since we have an operating window, flexibility exists to optimize efficiency

• Sometimes we use mathematical models for optimization (see 4G03 next semester)

• Sometimes we use plant experiments to optimize (see 4C03 next semester)

• Optimization can interact with other goals, such as consistent product quality. Therefore, we optimize slowly to prevent disturbing the processes.

Key Operability issues

1. Operating window


3. Reliability






EFFICIENCY

In this Lesson, we will learn

• The objective and degrees of freedom

• Improvement through equipment selection

- Pump/fluid flow

• Improvement through equipment utilization

- Pump/driver, boiler

• Improvement through process structure

- Ethylene plant, packed bed chemical reactor

• Improvement through operating conditions

- Fired heater/reactor, Flash, CSTR

Key Operability issues

1. Operating window


3. Reliability






process operability class materials process efficiency copyright © thomas marlin 2013 the copyright...

Documents

equipment capacity

safety equipment protection5

equipment protection4

sizing process equipment

operating window2

efficiency profitability6

flexibility controllability

dynamic performance8