POWER GENERATION SYSTEMS THAT UTILIZE WASTE HEAT IN CEMENT PLANTS

FOREWORD

• To day, in the world, even if most advanced cement kiln system, highest efficiency, large amount of thermal energy from the pre-heater and clinker cooler emits to the environment.
• Can make use of this thermal energy to generate electricity.
• Depending on the kiln technology, the moisture of the input mill that the amount of heat utilized can vary. Overall, a power generation system utilizing waste heat can meet 30% power needs of the plant.

Benefits of  power generation systems that utilize waste heat in cement plants, according to LBNL 2008, EPA 2010 reports:

• Reduce the amount of electricity purchased or reduce the dependence on self-generating power plants, reducing operating costs;
• Helps reduce pressure on electricity prices;
• Increase energy reliability for the plant;
• Increasing the competitive position of the factory in the market;
• Reduce energy consumption, reduce greenhouse gas emissions.

Overview about Power generation systems utilize waste heat

Technology diagram of a power generation system utilizing waste heat in cement plants

Classification of power generation systems utilizing waste heat

1. Steam Rankine Cycle (SRC)
2. Organic Rankine Cycle (ORC)
3. The Kalina cycle uses a mixture of water and a new promoter

1. Steam Rankine Cycle – SRC

• The most widely used system to date for cement plants, with the following characteristics:
• The most familiar to the cement industry, generally suitable for conditions of heat sources higher than 300 ° C
• Based on proven technologies and simple operation
• Available with multiple supplier
• Installation cost by investment rate (US $ / kW) is lower than other systems
• A high-temperature waste heat source is required for optimal operation (minimum 260 ° C) - the generation of electricity efficiency will be significantly reduced if the temperature is lower, also when steam pressure and temperature are low  can lead to partial condensation, eroding turbine blades.
• Typically, the waste heat from the clinker cooler is taken from the central wind of the cooler device to achieve an acceptable temperature for the system, but it means we have to accept some of the waste heat from the cooling equipment clinker will not be utilized.
• Full-time operating mode is required for this system, depending on local regulations.
• It is required to have a stable system of parameters of water supply.
• Condensers system are usually cooled by watet, wind-cooled condensers will affect system performance due to the need for deeper vacuum levels.
• This system is Good compatibility with high-capacity furnaces and low-humidity input furnaces (result is high exhaust temperature).

2. Organic Rankine Cycle - ORC

• Using work substances that are organic substances with large molecular weight such as butan, pentan.
• Low boiling point, high pressure steam
• Applicable to waste heat sources with a low temperature of about 150 oC (for steam systems, the minimum temperature must be 260 oC)
• Design with 2 levels of endothermic:

3. The Kalina cycle uses a mixture of water and amnonia

• The working substance is a mixture of 2 components: water and ammonia, which helps to increase the absorption heat efficiency.
• This system can Apply to waste heat source with low or fluctuating temperature.
• The system uses the Kalina cycle to have a very wide operating temperature range, which can receive heat sources from 95oC to 535oC.
• It is proved that 15% to 25% higher efficiency in ORC systems with the same temperature

Some technical characteristics of the system using Kalina cycle (according to Gibbon 2013, Mirolli 2012):

• Can be used for heat sources with lower temperatures than systems using conventional Steam Rankine cycles.
• This system has  Highly flexible, the system has a large operating range and can respond quickly in the event of a change in the temperature and flow of the exhaust gas.
• The water and ammonia mixture can be adjusted to achieve high thermal conductivity and high efficiency in proportion to temperature and flue gas flow.
• The working solvent mixture is not flammable
• This is a new technology that is in the stage of introduction to the market, so it has limited manufacturers and experience

Compare 2 diagrams between Rankine cycle diagrams and Kalina cycle

 Compiled by Cost Solutions Company Limited