Multiple technologies are used in the chemicals and plastics manufacturing sector including motors, pumps and fans, air compressors, boilers, lighting and heating, ventilation and air conditioning (HVAC) systems. Many plants have equipment that is used sub-optimally or is left on when not in use. Optimising the use of this equipment can yield energy savings for little or no cost.
By analysing energy use in terms of the throughput, it should be possible to determine if energy use per unit produced (for example, kWh per tonne) is broadly consistent during the day, week or month. This process can help identify opportunities for improved energy performance.
Motors systems are widely used in the chemicals sector to drive pumps, fans and air compressors. Because of their extensive use, they provide excellent opportunities for energy savings. It is also possible to cost effectively improve the energy efficiency of boilers and steam systems, as well as lighting and heating, ventilation and air conditioning systems.
The use of variable speed drives can in some cases result in up to 50% energy savings with a 3 year payback.
Optimising these technical systems, when coupled with best practice motor management, can generally deliver energy savings of between 30 to 60% cost effectively.
Many manufacturing plants have high energy overheads, such as equipment that is left on even when not in use. Ensuring that all equipment is turned off when not in use is a simple way to reduce energy usage.
The percentage yield and rate of chemical reactions is highly dependent on temperature and pressure. It may be possible to achieve energy savings through reviewing the optimal temperatures and pressures for particular chemical processes.
Ongoing innovations in catalysts can lower the activation energy barrier for chemical reactions, which reduces the temperatures and pressures needed.
Ensure chemical distillation is being carried out under optimum conditions and that the products are not being over-purified.
Decrease processing temperature, optimise cooling temperature and set thermostats to an appropriate temperature – a 1ºC drop in average space temperature can cut fuel consumption by about 8%. Be mindful that storing polymer granules at low temperatures can lead to the formation of condensation when the granules are moved into a warmer factory space. This can result in greater drying requirements prior to processing.
Monitor and adjust the pressure of equipment. Qenos reported through the EEO program – ‘The boiler feed water pumps produce a higher pressure than is needed to supply water to the furnace waste heat boilers. One of the boiler feedwater pumps is a steam turbine.’
‘Slowing the pump down will reduce steam usage by approximately 500kg/hr while still having adequate supply pressure for boiler feedwater. There is no capital investment required. Labour/engineering costs to implement will be less than $2000 and deliver an energy reduction of 12,000GJ and $30,000 per year in energy savings.'
Chemical and plastic process plants are complex and present an opportunity to minimise energy usage and maximise energy recovery through advanced process control (APC). APC is a systematic approach to enable dynamic optimisation of plant operations. APC involves installing hardware and software for capturing process operating data, analysing trends and developing strategies to optimise control of all relevant variables.
One of the most common processes in industrial chemical plants is distillation to separate chemical mixtures. Significant energy is used in this chemical separation processes because large quantities of steam need to be generated.
A substantial quantity of energy can be lost as heat through the production and distribution of steam requiring more energy to maintain boiler temperatures. Inefficient distillation and steam generation systems can also increase air-conditioning cooling loads.
Thermal insulation of pipes and taps and the replacement of defective steam traps are effective cost-saving measures in the distribution of steam. The amount of energy involved should also provide a strong incentive for minimising heat loss from boiler systems by insulating boiler valves, steam and condensate return pipes, and storage units.
A large proportion of energy used by chemical companies is related to the operation of furnaces and boilers. The efficient use of this equipment depends on good control and regular maintenance to reduce energy wastage in steam distribution.
The use of heat recovery is very common in the chemicals industry. Many of the processes used in the industry require extreme temperatures and often need rapid changes in temperature.
Heat and power recovery technologies offer significant potential to improve the energy efficiency of existing processes at chemical and plastics plants.
Recent innovations in the construction of heat exchangers has enabled heat to be recovered from processes that were previously too extreme to deal with, such as very high temperatures and pressures, and chemically hazardous environments. This has enabled more heat to effectively be captured and utilised in processes such as the manufacture of nitric acid or sodium hydroxide (caustic soda).
New generation heat pumps can be linked together to produce enough heat to make steam much more efficiently than traditional methods.
Boiler systems should have effective steam traps and condensate return. This saves water and helps to conserve the heat of the water in the boiler, because the returned condensate is much hotter than feedwater and may not require treatment.
For more information, see the Process heat and steam systems technology page.
Energy analysis and best practice case studies demonstrate that significant savings can be achieved through innovations in chemical and polymer manufacturing processes and upgrades to more energy-efficient equipment.
Steam cracking for olefin production is the most energy consuming process in the chemicals industry, but significant energy reductions are possible; for example, through the use of improved furnace and cracking tube materials. The remainder of the energy is used for separation of the ethylene product, typically by low-temperature distillation and compression. Up to 15% total energy can be saved in this process by improved separation and compression techniques, such as absorption technologies for separation. Catalytic cracking also offers the potential for reduced energy use, with a saving of up to 20% of total energy.
Plastic product manufacturers can achieve savings of more than 25% by upgrading equipment such extrusion machines, heating elements, ovens, and moulding machines. For example, polystyrene manufacturer Andpak (Aust) Pty Ltd based in Sunraysia, Victoria, has reduced energy use by 60% while also increasing production by more than 40%, through investment in more efficient moulding machines. The new moulding machines require significantly less steam than other technologies, requiring less energy to run.
Replacing factory high bay lighting with light emitting diodes (LED) units can also lead to substantial savings.
Importantly, replacing equipment provides an opportunity for further efficiencies by rationalising and redesigning outdated production processes and ensuring new equipment is correctly sized.
One of the most energy-intensive operations in the chemical industry is distillation separation. Most of the external energy and heat loss in distillation units occur in condensers, which are usually cooled by water or air. In many of the processes, a relatively few distillation columns and heat exchangers are responsible for the bulk of energy and heat losses.
These losses could be minimised by improved heat integration, such as cooling the condensers with other process streams or by using waste heat to raise steam.
Another approach is to use alternative separation technologies such as reactive distillation and membrane separation.
Energy assessments of the chemicals sector have shown the potential for significant energy savings from investing in co-generation. Studies in the US chemicals sector have found that combined heat and power systems, such as co-generation, could enable a 45% reduction in greenhouse gas emissions.
Solar water heating is well suited to help save energy by preheating boiler feedwater in steam boilers for a wide range of chemical and plastic manufacturing plants. Boiler feed can be heated in solar panels up to 80ºC before being fed to the boiler.
Larger combined solar thermal generators can concentrate enough energy from the sun to produce steam and electricity.