Selective Catalytic Reduction acid plants

Process Licensors. Some of the well-known nitric acid technology licensors are fisted in Table 3. Espindesa, Grande Paroisse, Humphreys and Glasgow, Rhfyne Poulenc, Uhde, and Weatherly are all reported to be licensors of weak acid technology. Most weak acid plant licensors offer extended absorption for NO abatement. Espindesa, Rhfyne Poulenc, Weatherly, and Uhde are also reported (53,57) to offer selective catalytic reduction (SCR) technology. 

Flue gas treatment (FGT) is more effective in reducing NO, emissions than are combustion controls, although at higher cost. FGT is also useful where combustion controls are not applicable. Pollution prevention measures, such as using a high-pressure process in nitric acid plants, is more cost-effective in controlling NO, emissions. FGT technologies have been primarily developed and are most widely used in Japan. The techniques can be classified as selective catalytic reduction, selective noncatalytic reduction, and adsorption. 

Nitric Acid Plant - Nitrogen oxide levels should be controlled to a maximum of 1.6 kg/t of 100% nitric acid. Extended absorption and technologies such as nonselective catalytic reduction (NSCR) and selective catalytic reduction (SCR) are used to eontrol nitrogen oxides in tail gases. 

Nitrous oxide has received increasing attention the last decade, due to the growing awareness of its impact on the environment, as it has been identified as an ozone depletion agent and as a Greenhouse gas [1]. Identified major sources include adipic acid production, nitric acid and fertilizer plants, fossil fuel and biomass combustion and de-NOx treatment techniques, like three-way catalysis and selective catalytic reduction [2,3]. 

A wide range of catalytic materials have been investigated for the selective catalytic reduction of NOx. For stationary emissions, NH3-SCR using vanadium-tungsten oxides supported on titania is the most used method however, when there is a simultaneous emission of NO and NOz (in tail gas from nitric acid plants), copper-based zeolites or analogous systems have been proven to be preferable [31b], In fact, there are two main reactions for NH3-SCR ... 

SOLINOX SO,. Linde NO,] A process for removing both NOx and SOx from fluegases. The SOx is removed by scrubbing with tetra-ethylene glycol dimethyl ether, circulated in a packed tower (the Selexol process). The NOx is destroyed by Selective Catalytic Reduction ( SCR). The sorbent is regenerated with steam the SOx is recovered for conversion to sulfuric acid. Developed by Linde in 1985 and used in a lead smelter in Austria and several power stations in Germany. In 1990 it was announced that it would be used at the titanium pigment plant in The Netherlands operated by Sachtleben. 

The primary pollution problem in nitric acid plants is the abatement of NOx in tail gases. Three options exist to reduce these emissions to acceptable levels 1) Capture the NOx and convert it to additional nitric acid, 2) Capture the NOx and convert it to nitrate-nitrite sales, or 3) Render the NOx harmless by converting it to non-polluting compounds. The processes that have been developed to reduce emissions at existing and new plants can be classified into four general categories Absorption, Adsorption, Selective Catalytic Reduction (SCR) and Non-Selective Catalytic Reduction91. 

Selective Catalytic Reduction (SCR) is normally used in new nitric acid plants. In this process ammonia reacts with nitric oxide and nitrogen dioxide but only to a lesser extent with oxygen to selectively reduce the NOx compounds to N2. The reactions are shown below97,104 ... 

Selective non catalytic reduction (SNCR) with NH3 is limited to industrial boilers in consequence of the relatively narrow temperature range for the reaction. Selective catalytic reduction (SCR) by ammonia has high efficiency and it can be used for many stationary sources, especially for nitric acid plants [1], and it is based on the catalytic pairing of nitrogen atoms, one fi-om nitric oxide, one fi om ammonia. This method, however, is imsuitable for small sources and vehicles. As far as automotive emission is concerned nonselective catalytic reduction (NSCR) by hydrocarbons, CO and H2 from the exhaust stream has been reported over various catalysts recently [1,3,4]. 

Selective Catalytic Reduction (SCR) [17] - Ammonia is used as a reducing agent over a catalyst to convert the NOx gases to nitrogen. These processes can reduce the concentration of NO in tail gas to 100 ppmv and lower. Existing plants with medium-pressure absorption can be economically revamped using this process. The capital cost of the selective catalytic reduction (SCR) process to remove NO from a concentration of 500-200 ppmv would increase the capital costs of a dual-pressure nitric acid plant by 2% and operational costs by US 0.30/tonne of nitric acid. The SCR method needs ammonia for reduction of NOx- The following reactions occur in the process of selective reduction of NO ... 

Figure 6.4.23 Single-pressure nitric acid plant (high pressure) using selective catalytic reduction (SCR) for NO f abatement (BFW boiler feed water). Adapted from Moulijn, Makkee, and Van Diepen (2004).

The accessibility of position 9 becomes much higher when an activating group, such as an OH, is present in position 10. Although 10-hydroxycamptothecin (8) is available in small amounts from the plant material, two efficient preparations of this compound were developed, via catalytic reduction of CPT in acid medium to a tetrahydroquinoline, followed by selective oxidation with lead tetraacetate [8], or phenyliodonium diacetate [27], or via a photochemical rearrangement of camptothe-... 

Postformation nitrogen oxide emission control measures include selective catalytic and noncatalytic reduction with ammonia, which between them are used by some 900 power station installations worldwide [51]. The catalytic removal methods are 70-90% efficient at NOx removal, but are more expensive to operate than the noncatalytic methods which are 30-80% efficient. Ammonia or methane noncatalytic reduction of NOx to elemental nitrogen is also an effective method which is cost-effective for high concentration sources such as nitric acid plants (Chap. 11). NOx capture in packed beds is less expensive, but this method is not particularly effective [23]. It is also not a very practical method either for utilities or for transportation sources. Two-stage scrubbing has also been proposed as an effective end-of-pipe NOx control measure. The first stage uses water alone and the second uses aqueous urea. 

---