ENERGY CONSERVATION IN CHEMICAL PROCESS INDUSTRIES Dr.V.SIVASUBRAMANIAN

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ENERGY CONSERVATION IN

CHEMICAL PROCESS

INDUSTRIES

Dr.V.SIVASUBRAMANIAN

Associate Professor

Former Head

Chemical Engineering

NIT Calicut

1

DEPARTMENT OF CHEMICAL

ENGINEERING

Agenda

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

11.

12.

Introduction

Energy Conservation in Reactors

Energy Conservation in Packed Beds

Energy Conservation in Heat Exchangers

Energy Conservation in Evaporators

Energy Conservation in Crushers and Grinders

Heating and Cooling Requirement in Distillation

Columns

Energy Conservation in Dryers

Energy Conservation in Pumps

Methodology of Optimizing Energy Use

Areas of energy Optimization in CPI

Energy Efficiency Improvement and Cost Saving

Opportunities in Petrochemical Industry

3

1. Introduction

CHEMICAL

PROCESS

UNIT

PROCESS

UNIT

OPERATION

CHEMICAL ENGINEERING DEPT NIT CALICUT

4

Figure I

Input

– Processing – Output

System

RECYCLE

DISPOSAL

WASTE

INPUT

PROCESSING

OUTPUT

CHEMICAL ENGINEERING DEPT NIT CALICUT

Chemical Reaction Types in

Petrochemical Industries

1 Pyrolysis 16 Oxidation

2 Alkylation

3 Hydrogenation

4 Dehydration

5 Hydroformylation

6 Halogenation

7 Hydrolysis/Hydration

8 Dehydrogenation

9 Esterification

10 Dehydrohalogenation

11 Ammonolysis

12 Reforming

13 Oxyhalogenation

14 Condensation

15 Cleavage

17 Hydrodealkylation

18 Isomerization

19 Oxyacetylation

20 Oligormerization

21 Nitration

22 Hydrohalogenation

23 Reduction

24 Sulfonation

25 Hydrocyanation

26 Neutralization

27 Hydrodimerization

28 Miscellaneous

29 Nonreactor processes

U.S.-EPA (1993) 6

Unit Operations

Liquid-vapor stripping) separation (distillation, evaporation,

Liquid-liquid separation (extraction, decanting)

Solid-liquid separation (centrifugal, filtration)

Solid-gas separation (filtration)

Solid-solid separation (screening, gravity)

CHEMICAL ENGINEERING DEPT NIT CALICUT 7

2.Energy Conservation in Reactors

Ideal Reactors

(a) Batch reactor, or BR (b) Plug flow reactor, or PFR and

(c) Mixed flow reactor, or MFR

8

Broad Classification of Reactor

Types

(a) The batch reactor. (b) The steady-state

flow reactor. (c),

(d), and

(e) Various forms of the semibatch reactor

CHEMICAL ENGINEERING DEPT NIT CALICUT 9

Material Balance for the

Element of Volume of Reactor

10

Material Balance for the

Element of Volume of Reactor

11

Energy Balance for the Element of Volume of Reactor

12

Energy Balance for the Element of Volume of Reactor

13

AGITATION PROCESS VESSEL

14

Mixing Impellers

(a) three-blade marine propeller; (b) open straight-blade

turbine; (c) bladed disk turbine; (d) vertical curved-blade

turbine; (e) pitched-blade turbine

15

Design of Agitated Vessel

16

17

Power Consumption in Agitated

Vessel

•Np power no.

•P power in kW

•gc Newton’s law proportionality factor

•n rotational speed r/s

•Da diameter of impeller in m

 density in kg/m

3

18

Power Correlation

•S1, S2, Sn – Shape factors

•hc individual htc for outside of coil, W/m

2

-

C

•Dc outside dia of coil tubing, m

•k thermal conductivity, W/m-

C

•Cp specific heat @constant pressure, J/g-

C

 absolute viscosity, cP

 w absolute viscosity @wall or surface temp

19

Swirling flow pattern with a radialflow turbine in an unbaffled vessel

20

Prevention of Swirling

21

Multiple turbines in tall tanks

22

Draft tubes, baffled tank

(a) Turbine (b) propeller

23

Energy Efficiency in Reactors

Agitator motor current monitoring:

VFD deployment

–feasibility.

Accurate mass transfer for reaction by mass flow meters or vortex/magnetic flow meters.

Recovery

Reaction of heat in case of Exothermic

Batch within

–Automation to control the reaction a consumed.

narrow range, saving energy

3. Energy Conservation in

Packed Beds

Nusselt Number hw individual htc of gas film near tube wall

Dp diameter of particle k g thermal conductivity of gas

Prandtl Number,

25

4. Energy Conservation in Heat

Exchangers

Single pass tubular condenser

26

27

Energy Balance in Heat

Exchangers

flow rate of stream

q = Q/t = rate of heat transfer into stream

Ha, Hb enthalpies per unit mass of stream at entrance and exit

28

EXTENDED SURFACE

EQUIPMENT

Types of extended surface: (a) longitudinal fins;

(b) transverse fins.

29

5. Energy Conservation in

Evaporators

•Types of Evaporators

30

Climbing-film, long-tube vertical evaporator

31

Evaporator Capacity and

Economy

q rate of heat transfer through heating surface from steam

Hs specific enthalpy of steam

Hc specific enthalpy of condensate

s latent heat of condensation of steam

rate of flow of steam

32

Methods of Feeding in Evaporator

Patterns of liquor flow in multiple~effect evaporators:

(a) forward feed

(b) backward feed

(c) mixed feed

(d) parallel feed

33

6. Energy Conservation in

Crushers and Grinders

•Rittinger’s Law

•Kick’s Law

•Bond’s Law

34

7. Heating and Cooling Requirement in Distillation Column

If saturated steam is used as the heating medium, the steam required at the reboiler

 s

steam consumption

vapor rate from reboiler

latent heat of steam molal latent heat of mixture

35

•If water is used as the cooling medium in the condenser and the condensate is not subcooled, the cooling-water requirement is

water consumption

T2 - Tl = temperature rise of cooling water

36

8. Energy Conservation in

Dryers

Tray Dryer

37

Temperature Patterns in Dryers

(a) batch dryer

(b) continuous countercurrent adiabatic dryer

38

Calculation of Heat Duty

Heat transferred per unit mass of solid

39

9.ENERGY

CONSERVATION IN

PUMPS

40

www.enviro-stewards.com

49

10.

Methodology of Optimizing

Energy Use

1.

Measure and benchmark consumption. Compare with globally accepted norms.

2.

Carryout energy audit and energy balance.

3.

Examine availability of more energy efficient processes and equipment with higher efficiencies.

Implement new technologies bringing in a reduction in energy & raw material consumptions.

4.

Reduce cycle time by eliminating non-value adding activities.

58

5.

Identify areas of losses and plan methods to reduce losses.

6.

Reuse waste, harness waste streams.

7.

Replace higher form of energy use by low grade / low cost / renewable energy.

8.

Minimize transmission losses.

9.

Measure and control.

59

11.

Areas of energy

Optimization in CPI

1. BOILERS AND STEAM USAGE a.

b.

c.

d.

e.

For Solid fuel fired boilers: Convert stoker fired boilers to FBC

Optimize excess air. Provide continuous monitoring with auto adjustment of oxygen trim in large boilers and periodical checking in smaller boilers.

Preheat combustion air with waste heat

Install variable frequency drives (VFD) on large boiler combustion air fans having variable loads.

Burn waste stream if permitted, use bio waste like coconut kernel, rice husk, instead of conventional fuels.

60

f.

g.

h.

i.

j.

Recycle condensate.

Recover flash condensate.

steam from higher pressure

Pass steam through back pressure steam turbine rather than through pressure reducing station for low pressure steam.

Attend steam insulation.

leakages and repair damaged

Examine possibility of installation of cogeneration systems (combined electricity and steam generation)

/ trigeneration system (combined electricity, steam & refrigeration generation)

61

2. PUMPS

a.

b.

c.

d.

Select the right pump to match head and flow requirements.

Make maximum intermediate use storages of to gravity avoid flow.

pumping.

Avoid

For circulation system use siphon effect; avoid free fall

(gravity) return.

Avoid throttling / bypass; to control flow, prefer speed controls or sequenced operation of pumps.

In pumping to systems having a number of noncontinuous users, auto ON-OFF valves / control valves need to be provided on users and VFD on pumps.

62

f.

g.

h.

i.

Segregate high head and low head loads and install separate pumps.

Operate booster pumps for small loads requiring higher heads, in place of operating complete system at higher head.

Operator cooling/chilling system with higher fluid differential temperature to decrease flow and hence save pumping energy.

Replace old pumps by high efficiency pumps.

63

j.

k.

l.

Trim impellers wherever pumps are over designed.

Valve throttling indicates pump over design; replace pump with correct size pump or install lower size impeller

Coat hydraulic passages of pumps with resins having better surface finish to reduce internal friction and increase efficiency.

m.

Minimize pressure drop in piping by rerouting of pipeline, removing valves, which never need to be operated, and resizing of pipeline.

64

3. COOLING TOWERS

a.

b.

c.

d.

e.

Control CT fans based on cold well temperature; use two speed or VFD if fans are few and on-off stage control if cells are many.

Select CT with low pressure drop, high efficiency

PVC cellular fills in place of splash bars.

Periodically clean, water distribution nozzles. Ensure that no channeling of water flow is taking place.

Uniform flow distribution will improve performance of cooling tower.

Optimize cooling water chemical treatment.

Replace aluminum fans by aerodynamic FRP fans.

65

4. REFRIGERATION

SYSTEMS

a.

Challenge the need of refrigeration system, particularly, for old batch processes. Optimise the temperature requirement.

b.

Examine the possibility of vapour absorption system operating with waste heat streams in place of vapour compression systems.

c.

Check regularly for correct refrigerant charge levels.

66

d.

Check for damaged insulation / sweating.

e.

Select multistage compressors with inter cooling for low temperature applications.

f.

Operate chillers with lowest possible condensing temperature and highest possible chiller

(evaporator) temperature.

g.

Carryout regular cleaning of condenser to ensure proper heat transfer.

67

5. LIGHTING

a.

Select high efficiency lighting luminaries having highest lumens / watt output.

eg.

Compact fluorescent lamp (CFL), low pressure sodium vapour lamp.

b.

Provide lighting transformer to reduce the voltage of lighting loads.

c.

Make use of task lighting.

d.

Make most use of day lighting by providing skylight.

68

e.

Paint walls and ceiling with light colors.

f.

Lower height of light fixtures.

g.

Control lighting with clock timers, sensors, photocells and master switch.

occupancy h.

Select ballast with high efficiency and high power factors.

i.

Use LED lamps for indicating purpose.

69

6. FANS & BLOWERS

a.

Select fans with aerofoil fan blades; replace old inefficient fans by modern high efficincy fans / blowers.

b.

Ensure that design of fans / blowers are matching with operating conditions if not replace with correct size fan / blower.

c.

Replace throttle / bypass control by speed control.

70

d.

Minimize speed to minimum possible.

e.

Reduce pressure drops in system by proper design / sizing of ducting. Minimize bends in ductings.

f.

Eliminate leakages.

g.

Clean screen, filters, fan blades regularly.

h.

Avoid idle running of fans by interlocking with main equipments.

71

7. MOTORS

a.

Properly size the motor for the optimum efficiency.

b.

Use energy efficient motors for continuous operating loads.

c.

Balance three phase loads. An imbalanced voltage can reduce efficiency of motor by 3-5%.

d.

Connect motors remaining under loaded (< 40%) continuously, in star.

72

e.

Rewound motors should be checked for efficiency.

f.

g.

Provide capacitor banks at MMC to correct PF.

Use soft starters / VFD instead of fluid coupling for loads having high starting torque or loads prone to jamming.

73

12. Energy Efficiency

Improvement and Cost

Saving Opportunities in

Petrochemical Industry

74

The U.S. Petrochemical

Industry

The North American Industry Classification (NAICS) distinguishes seven 4-digit sub-sectors of the chemical industry:

• 3251 Basic chemical manufacturing

• 3252 Resin, synthetic rubber, and artificial synthetic fibers and filaments manufacturing

• 3253 Pesticide, fertilizer and other agricultural chemical manufacturing

• 3254 Pharmaceutical and medicine manufacturing

• 3255 Paint, coating, and adhesive manufacturing

• 3256 Soap, cleaning compound, and toilet preparation manufacturing

• 3259 Other chemical product and preparation manufacturing

75

Supporting Equipment and

Infrastructure

•Emission abatement equipment.

•Product storage and handling equipment

•Boilers, Combined Heat and Power (CHP) plants and other parts of the steam infrastructure including pipes and valves.

•Furnaces and process heaters.

•Pumps, compressors, vacuum, pressure relief equipment and fans.

•Heat exchangers, cooling and refrigeration.

76

Energy use in the chemical industry by fuels and feedstock category, 2002

77

Energy use by sub-sector,

2002

78

End use of electricity in the total chemical industry and the subsectors studied, 2002

79

Estimated final energy consumption for selected key chemicals

80

Main elements of a strategic energy management program

81

Simplified schematic of a steam production and distribution system

82

Summary of energy efficiency measures in boilers (Steam Supply)

83

Steam Supply - Combined

Heat and Power

Steam injected gas turbines

High-temperature CHP

Steam expansion turbines

84

Summary of energy efficiency measures in steam distribution systems

85

Furnaces and Process Heaters

•Heat Generation

•Control the air-fuel ratio

•Excess air should be limited to 2-3% oxygen

86

Heat transfer and heat containment in heaters

•Use of soot blowers, burning off carbon and other deposits from radiant tubes and cleaning the heat exchange surfaces. Typical savings are 5-10%.

•Ceramic coated furnace tubes can improve heat transfer

•Reducing wall heat losses (typical savings 2-5%), furnace pressure control (5-10%), maintenance of door and tube seals (up to 5%), reducing cooling of internal parts (up to 5%) and reducing radiation heat losses (up to 5%).

87

Flue gas heat recovery

Others

– controls, maintenance and electric heaters

88

Electric Motors

Motor Management Plan

•Creation of a motor survey and tracking program.

•Development of guidelines for proactive repair/replace decisions.

•Preparation for motor failure by creating a spares inventory.

•Development of a purchasing specification.

•Development of a repair specification.

•Development and implementation of a predictive and preventive maintenance program.

89

•Strategic motor selection

•Maintenance

•Properly sized motors

•Adjustable speed drives

•Power factor correction

•Minimizing voltage unbalances

90

Pumps

Operations and maintenance

Monitoring

Reduce need

More efficient pumps

Correct sizing intended duty) of pump(s) (matching

Use multiple pumps

Trimming impeller (or shaving sheaves)

Controls pump to

91

Adjustable speed drives (ASDs)

Avoid throttling valves

Correct sizing of pipes

Replace belt drives

Precision castings, surface coatings or polishing

Sealings

Curtailing leakage through clearance reduction

Dry vacuum pumps

92

Fans and Blowers

Fan oversizing

Adjustable speed drives (ASDs) and improved controls

High efficiency belts (cog belts)

93

Compressors and Compressed

Air Systems

•Compressed air – maintenance

•Monitoring

•Reduce leaks (in pipes and equipment)

•Reducing the inlet air temperature

•Maximize allowable pressure dew point at air intake

•Optimize the compressor to match load

•Controls

•Properly sized regulators

•Sizing pipe diameter correctly

•Heat recovery for water or space heating preheating

•Adjustable speed drives (ASDs)

•High efficiency motors

94

Distillation

•Enhanced distillation controls

•Optimization of reflux ratios

•Check product purity

•Seasonal operating pressure adjustments

•Column insulation

•Reducing reboiler duty

•Feed conditioning

•Upgrading column internals

•Stripper optimization

95

Buildings: HVAC and Lighting

Energy Efficiency Measures for HVAC Systems

•Energy efficient system design

•Recommissioning

•Energy monitoring and control systems

•Non-production hours set-back temperatures

•Duct leakage repair

•Variable-air-volume systems

•Adjustable-speed drives (ASDs)

•Heat recovery systems

•Fan modification

•Efficient exhaust fans

•Use of ventilation fans

•Cooling water recovery

•Solar air heating

•Building reflection

•Building insulation

•Low emittance (Low-E) windows

96

Energy Efficiency Measures for

Lighting

•Turning off lights in unoccupied areas

•Lighting controls

•Exit signs

•Electronic ballasts

•Replacement of T-12 tubes with T-8 tubes

•Replacement of mercury lights

•High-intensity discharge (HID) voltage reduction

•High-intensity fluorescent light

•Daylighting

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CONCLUSIONS

•A key first step in any energy improvement initiative is to establish a focused and strategic energy management program , which will help to identify and implement energy efficiency measures and practices across and organization and ensure continuous improvement.

• While the expected savings associated with some of the individual measures may be relatively small, the cumulative effect of these measures across an entire plant may potentially be quite large.

•The degree of implementation of these measures will vary by plant and end use ; continuous evaluation of these measures will help to identify further cost savings in ongoing energy management programs.

98

ACKNOWLEDGEMENT

Octave Levenspiel, Chemical

Engineering, Wiley Eastern Limited.

Reaction

McCabe, W.L. and Smith, J.C., Unit Operation of

Chemical Engineering, McGraw Hill, New York.

Internet sources

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THANK YOU

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