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ENERGY CONSERVATION IN CHEMICAL PROCESS

INDUSTRIES

Dr.V.SIVASUBRAMANIAN

Associate ProfessorFormer HeadChemical EngineeringNIT Calicut

DEPARTMENT OF CHEMICAL ENGINEERING

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Agenda1. Introduction2. Energy Conservation in Reactors3. Energy Conservation in Packed Beds4. Energy Conservation in Heat Exchangers5. Energy Conservation in Evaporators6. Energy Conservation in Crushers and Grinders7. Heating and Cooling Requirement in Distillation

Columns8. Energy Conservation in Dryers9. Energy Conservation in Pumps10. Methodology of Optimizing Energy Use11. Areas of energy Optimization in CPI12. Energy Efficiency Improvement and Cost Saving

Opportunities in Petrochemical Industry

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1. IntroductionCHEMICAL PROCESS

UNIT PROCESS

UNIT OPERATION

CHEMICAL ENGINEERING DEPT NIT CALICUT

Figure I Input – Processing – Output

System

•RECYCLE

WASTE

INPUT PROCESSING OUTPUT

DISPOSAL

CHEMICAL ENGINEERING DEPT NIT CALICUT

Chemical Reaction Types in Petrochemical Industries

1 Pyrolysis 16 Oxidation

2 Alkylation 17 Hydrodealkylation

3 Hydrogenation 18 Isomerization

4 Dehydration 19 Oxyacetylation

5 Hydroformylation 20 Oligormerization

6 Halogenation 21 Nitration

7 Hydrolysis/Hydration 22 Hydrohalogenation

8 Dehydrogenation 23 Reduction

9 Esterification 24 Sulfonation

10 Dehydrohalogenation 25 Hydrocyanation

11 Ammonolysis 26 Neutralization

12 Reforming 27 Hydrodimerization

13 Oxyhalogenation 28 Miscellaneous

14 Condensation 29 Nonreactor processes

15 Cleavage  

U.S.-EPA (1993) 6

Unit Operations

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•Liquid-vapor separation (distillation, evaporation,

stripping)

•Liquid-liquid separation (extraction, decanting)

•Solid-liquid separation (centrifugal, filtration)

•Solid-gas separation (filtration)

•Solid-solid separation (screening, gravity)

CHEMICAL ENGINEERING DEPT NIT CALICUT

Ideal Reactors

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

(c) Mixed flow reactor, or MFR

2.Energy Conservation in Reactors

Broad Classification of Reactor Types

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(a) The batch reactor. (b) The steady-state flow reactor. (c), (d), and (e) Various forms of the semibatch reactor

Material Balance for the Element of Volume of Reactor

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Material Balance for the Element of Volume of Reactor

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Energy Balance for the Element of Volume of Reactor

Energy Balance for the Element of Volume of Reactor

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AGITATION PROCESS VESSEL

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Mixing Impellers

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•(a) three-blade marine propeller; (b) open straight-blade turbine; (c) bladed disk turbine; (d) vertical curved-blade turbine; (e) pitched-blade turbine

Design of Agitated Vessel

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Power Consumption in Agitated Vessel

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•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/m3

Power Correlation

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•S1, S2, Sn – Shape factors

•hc individual htc for outside of coil, W/m2-C•Dc outside dia of coil tubing, m•k thermal conductivity, W/m-C•Cp specific heat @constant pressure, J/g-C absolute viscosity, cPw absolute viscosity @wall or surface temp

Swirling flow pattern with a radial-flow turbine in an unbaffled vessel

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Prevention of Swirling

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Multiple turbines in tall tanks

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Draft tubes, baffled tank

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(a) Turbine (b) propeller

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 of heat in case of Exothermic Reaction

Batch –Automation to control the reaction within a narrow range, saving energy consumed.

3. Energy Conservation in Packed Beds

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Nusselt Number

hw individual htc of gas film near tube wall

Dp diameter of particle

kg thermal conductivity of gas

Prandtl Number,

4. Energy Conservation in Heat Exchangers

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Single pass tubular condenser

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Energy Balance in Heat Exchangers

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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

EXTENDED SURFACE EQUIPMENT

Types of extended surface: (a) longitudinal fins;

(b) transverse fins.29

5. Energy Conservation in Evaporators

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•Types of Evaporators

Climbing-film, long-tube vertical evaporator

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Evaporator Capacity and Economy

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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

Methods of Feeding in Evaporator

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•Patterns of liquor flow in multiple~effect evaporators: •(a) forward feed•(b) backward feed •(c) mixed feed •(d) parallel feed

6. Energy Conservation in Crushers and Grinders

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•Rittinger’s Law

•Kick’s Law

•Bond’s Law

7. Heating and Cooling Requirement in Distillation Column

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steam consumption

vapor rate from reboiler

s latent heat of steam

molal latent heat of mixture

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

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•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

8. Energy Conservation in Dryers

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Tray Dryer

Temperature Patterns in Dryers

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(a) batch dryer

(b) continuous countercurrent adiabatic dryer

Calculation of Heat Duty

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Heat transferred per unit mass of solid

9.ENERGY CONSERVATION IN

PUMPS

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10. Methodology of Optimizing Energy Use

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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.

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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.

11. Areas of energy Optimization in CPI

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

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

c. Preheat combustion air with waste heat

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

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

1. BOILERS AND STEAM USAGE

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f. Recycle condensate.

g. Recover flash steam from higher pressure condensate.

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

i. Attend steam leakages and repair damaged insulation.

j. Examine possibility of installation of cogeneration systems (combined electricity and steam generation) / trigeneration system (combined electricity, steam & refrigeration generation)

2. PUMPS

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a. Select the right pump to match head and flow requirements.

b. Make maximum use of gravity flow. Avoid intermediate storages to avoid pumping. For circulation system use siphon effect; avoid free fall (gravity) return.

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

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

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

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

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

i.Replace old pumps by high efficiency pumps.

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j. Trim impellers wherever pumps are over designed.

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

l. 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.

3. COOLING TOWERS

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a. 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.

b. Select CT with low pressure drop, high efficiency PVC cellular fills in place of splash bars.

c. Periodically clean, water distribution nozzles. Ensure that no channeling of water flow is taking place. Uniform flow distribution will improve performance of cooling tower.

d. Optimize cooling water chemical treatment.

e. Replace aluminum fans by aerodynamic FRP fans.

4. REFRIGERATION SYSTEMS

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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.

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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.

5. LIGHTING

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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.

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e. Paint walls and ceiling with light colors.

f. Lower height of light fixtures.

g. Control lighting with clock timers, occupancy

sensors, photocells and master switch.

h. Select ballast with high efficiency and high power

factors.

i. Use LED lamps for indicating purpose.

6. FANS & BLOWERS

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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.

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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.

7. MOTORS

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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.

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e. Rewound motors should be checked for efficiency.

f. Provide capacitor banks at MMC to correct PF.

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

12. Energy Efficiency Improvement and Cost Saving Opportunities in Petrochemical Industry

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The U.S. Petrochemical Industry

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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

Supporting Equipment and Infrastructure

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•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.

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

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Energy use by sub-sector, 2002

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End use of electricity in the total chemical industry and the sub-sectors studied, 2002

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Estimated final energy consumption for selected key chemicals

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Main elements of a strategic energy management program

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Simplified schematic of a steam production and distribution system

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Summary of energy efficiency measures in boilers (Steam Supply)

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Steam Supply - Combined Heat and Power

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•Steam injected gas turbines

•High-temperature CHP

•Steam expansion turbines

Summary of energy efficiency measures in steam distribution systems

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Furnaces and Process Heaters

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•Heat Generation

•Control the air-fuel ratio

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

Heat transfer and heat containment in heaters

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•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%).

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•Flue gas heat recovery

•Others – controls, maintenance and electric heaters

Electric Motors

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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.

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•Strategic motor selection

•Maintenance

•Properly sized motors

•Adjustable speed drives

•Power factor correction

•Minimizing voltage unbalances

Pumps

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•Operations and maintenance•Monitoring•Reduce need•More efficient pumps•Correct sizing of pump(s) (matching pump to intended duty)•Use multiple pumps•Trimming impeller (or shaving sheaves)•Controls

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•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

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•Fan oversizing

•Adjustable speed drives (ASDs) and improved controls

•High efficiency belts (cog belts)

Fans and Blowers

Compressors and Compressed Air Systems

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•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

Distillation

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•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

Buildings: HVAC and LightingEnergy Efficiency Measures for HVAC Systems

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•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

Energy Efficiency Measures for Lighting

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•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

CONCLUSIONS

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•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.

ACKNOWLEDGEMENT

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Octave Levenspiel, Chemical Reaction

Engineering, Wiley Eastern Limited.

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

Operation of Chemical Engineering, McGraw Hill,

New York.

Internet sources

THANK YOU