Cement, Energy and Environment

39 supervised at the superior control system (DCS) of the plant. The system can be equipped with a VPN connection for remote control, trimming and supervision from the supplier. Installation and commissioning The installation of a SNCR system does not require any modifications on the cement plant. Just some holes in the preheater / precalciners. If the SNCR equipment is standardized, and built in prefabricated well proven modules, the engineering time and time for installation and commissioning is quite short. The installation works on site requires piping for reagent, water and compressed air between the modules. The pipes for the reagent shall be made in stainless steel. The electrical works are limited to power connection of the modules and communication cables between them and to the DCS. 4.0 Ammonia or urea? So far there are two different types of reagents that have been used in SNCR systems.  Ammonium hydroxide - NH 4 OH Also named ammonia solution or aqueous ammonia. The concentration is commonly <25% due to hazard classification and safety and transport regulations.  Urea - NH 2 CONH 2 Is used in different concentrations, typically from 30 – 40%. Most commonly delivered in liquid form in tank trucks to the cement plant. Some plants are receiving dry urea and have on site a dissolving station, mixing the dry urea with warm and softened water. The dry urea can be delivered in bulk or in big bags. The urea has to be of technical grade. Fertilizer grade may have impurities that can jeopardize the functioning of the SNCR system. Which one to use? There are several aspects to take into account when choosing the reagent.  The availability and price of product. Transport cost can be a significant part of the price for long transport distances.  The reduction needed. With urea, reductions of 20-50% are possible depending on the process conditions. With ammonia, much higher reductions can be reached, even up to 90% if the process conditions are the suitable ones.  The chemical efficiency and its effect on the OPEX. Ammonia is about 2-3 times more efficient than urea. This is based on a large number of comparative test injections and references done by Yara.  Ammonia slip requirements. Urea gives higher ammonia slip than ammonia.  Urea gives higher emission of laughing gas (N 2 O) than ammonia. Laughing gas is a greenhouse gas, 300 times more potent than CO 2 .  A flexible SNCR system that can run on both ammonia solution and urea solution. Will give flexibility in the use of reagent depending on variation in supply and price conditions.  Tank and piping for urea will need freezing protection.  Local safety regulations and permissions for storage and handling. To reach this high reduction, the SNCR installation has to be efficient and ammonia solution should be used. Some of the main factors that make a SNCR installation efficient are:  The use of ammonia solution.  The right number of injectors at the right locations that have the most favorable process conditions. Temperature, time, end of combustion.  The number of injectors and their locations should also give flexibility for changes of fuel and changes in the process.  Injector design. We have seen up to 20 – 30% efficiency difference comparing different injectors.  The control system and its software. It should be fully automatic and should quickly respond to the variations in NOx and other conditions.  The experience of the supplier. *****