Energy efficiency in heating systems in industry and production
Many industrial production processes and methods require large quantities of process heat and this usually entails considerable energy costs for the businesses. Comprehensive energy optimisation of a heating system can considerably reduce energy consumption and costs for combustion plants, on average by 15 percent. Such energy efficiency measures are highly costeffective and generally pay for themselves within one to four years.
Approach to system optimisation
Measures for increasing energy efficiency in a heating system should always be regarded as part of the optimisation of the complete system because the greatest increases in energy efficiency can be achieved by matching all the components to one another and optimising the plant’s control systems.
If effective energy saving measures are to be devised, the first step should be to carry out a detailed actual analysis of the system’s energy consumption, its heating demand and its individual system components. Then the energy efficiency of the individual components should be checked so that any old componen ts, such as burners, can be replaced if necessary. Further savings can be achieved by optimising the combustion plant’s control systems. When constructing new systems, attention should be paid from the outset to the energy efficiency of the components and of the overall system.
1. Minimise demand and losses
Before optimising the individual components of a heating system, steps should first of all be taken to minimise heating demand and losses. Electrical energy should here be ranked as more valuable than steam and steam as more valuable than hot water. Depending on requirements, the lowest value energy supply medium should thus be selected for each process step. Efficiency can be raised by 10 to 15 percent just by using warm water instead of steam. In many cases, reducing the temperature of the supply medium makes it possible to use heat recovery and cogeneration to reduce energy requirements still further.
In order to minimise losses, the thermal insulation on heat generators, pipework and any heat stores should be checked and, if necessary, repaired.
2. Use heat recovery
Heat recovery measures maximise the efficiency of the overall system and thus increase its energy efficiency. As a rule of thumb, heat recovery becomes more worthwhile the greater is the difference between the waste heat temperature and the required temperature.
Heat potential should be used locally and as directly as possible. Waste heat may be put to further use for heating process water, for water heating, for preheating combustion and drying air or as space heating. It is advisable, for example, to use an economiser for preheating feed water. In condensing boiler technology, an additional heat exchanger is provided downstream of the economiser. This heat exchanger cools the flue gases to below the condensing temperature of water, so making it possible to utilise the heat of condensation of the water present in the flue gas.
3. Use energy-efficient components
Even when energy-efficient components are used, the goal should always be to optimise the entire system. This is achieved by effectively matching all new and existing components to one another.
Modulating (controllable) burners may be used over extensive partial load ranges. They are substantially more efficient than burners which are switched on and off individually.
Flue gas temperatures and energ y consumption can be reduced thanks to boilers with large heat exchange areas. It is advisable to use energy-efficient condensing boilers for warm water systems because such boilers give rise to considerably lower flue gas temperatures and they operate at a distinctly higher level of efficiency.
Speed-controlled drive motors for forced-draught burners and pumps enable considerable savings in energy consumption.
4. Optimise control systems
Combustion plants should in principle be designed on the basis of the actual heating demand. For instance, a multi-boiler control system ensures that only the necessar y number of boilers is switched on in accordance with requirements.
If a flue gas sensor control system is installed, the flue gas composition can be continuously measured. Air feed is controlled on the basis of the optimum oxygen (O2) content in the flue gas. Reducing the O2 content by just one percent results, depending on the age of the system, in a 0.5 to 1 percent improvement in efficiency. Energy consumption can be further reduced by monitoring and controlling further combustion parameters such as CO content, flue gas temperature, soot index or combustion chamber pressure and by installing automatic flue gas or combustion dampers.
Source: factsheet by Deutsche Energie-Agentur (DENA) Initiative EnergieEffizienz campaign and the Bundesindustrieverband Deutschland Haus-, Energie- und Umwelttechnik e. V. (BDH)
