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Abatement of urea dust and gaseous ammonia emissions

Summary

In modern urea plants, the main pollution to the environment originates from the prilling or granulation finishing section. In recent years there has been a growing interest in technologies to reduce the urea dust and gaseous ammonia emissions from prilling towers and granulation units. Wet processes are generally applied. The available technologies vary with regards to the scrubber design, type of demisters and the gas moisturising/spraying system.

Abstract

Technology solutions for the abatement of urea dust and gaseous ammonia emissions from urea plants have been booming in recent years. From an environmental point of view, a urea plant can be divided into two sections:

  • The wet section, which produces a urea melt or concentrated solution. The wet section comprises the urea synthesis section, decomposition and recirculation stages, evaporation or crystallisation sections and waste water treatment.
  • The finishing section, where the urea melt from the wet section is solidified typically by prilling or granulation, ready for transportation from the plant.

In modern urea plants, the main pollution to the environment originates from the prilling or granulation finishing section1. For urea product size of less than approx 3 mm, prilling technology is used and for a larger product size, granulation technology is applied.

Exit air from urea prilling towers and especially granulators contains urea dust in quantities far above the limits defined in current regulations concerning environment protection. The air also contains gaseous ammonia and again, its concentration in most cases does not comply with the law (Table 1).

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Improving the energy efficiency of AN solution plants

Summary

The ammonium nitrate (AN) neutralisation process is a major chemical process, especially serving the fertiliser industry. The development of AN neutralisation plants has been largely determined by the goal of designing a safe, reliable and well controlled process. In this article, A. Erben and Dr. K. Ruthardt of Uhde GmbH discuss the options for energy utilisation and recovery and relate them to other aspects of plant design and operation.

Abstract

The first known synthesis of ammonium nitrate (from ammonium carbonate and nitric acid) dates back to the 17th century. Industrial production, however, was not possible until the early 20th century when the invention of the Ostwald process for nitric acid and the Haber-Bosch process for ammonia made it possible to provide sufficient raw materials.

Uhde was founded by Friedrich Uhde in 1921 and was a pioneer in the development of proprietary processes for ammonia and nitric acid. In 1952 Uhde built and commissioned the first AN solution plant for Norddeutsche Chemische Werke GmbH in Embsen, Germany, based on a neutralisation tower design. But it wasn’t until 1967, after designing several AN plants, that the present design was developed with respect to safety and an increased efficiency for raw materials and energy consumption. It incorporates several patented and proprietary items. Over the decades the process has been further developed to the current design and variants. More than 30 AN neutralisation plants have been designed and built with plant capacities ranging from 100 to 2,300 t/d of 100% AN.

The Uhde AN neutralisation processes follow one design principle, but three main variants have been developed and commercialised, driven by different requirements for energy efficiency and use.

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Syngas to power

Summary

While syngas is a versatile mix of chemicals, one of the simplest ways of using it is simply to burn it. Integrated Gasification Combined Cycle plants have been touted as a 'clean coal' technology for power generation, and are beginning to see a renewed wave of interest.

Abstract

Integrated Gasification Combined Cycle (IGCC) technology is a power production technology using syngas. A simplified flow diagram is shown in Figure 1. Coal and/or petroleum coke is pulverised and fed into the gasifier along with oxygen that is produced in an on site air separation unit. The combination of heat, pressure, and steam breaks down the feedstock and creates chemical reactions that produce a hydrogen and carbon monoxide synthesis gas. Feedstock minerals become an inert, glassy slag product, recoverable from the bottom of the gasifier to be used in road beds, landfill cover, and other applications.

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Syngas in North America

Summary

Lower natural gas prices from the US shale gas boom have changed the outlook for North American producers of ammonia, methanol and other syngas products. But is this a lasting change or just a temporary respite?

Abstract

Up to 2008, received wisdom was that rising US natural gas prices would price gas-based chemical capacity out of the market, with considerable interest revived in heavy feedstocks like coal, petroleum coke and potentially biomass. However, the rising demand for gas and power that had fed the booming gas prices has been cut back – possibly by a few years – by the recent recession, and the commodity bubble had also served to mask a transformation that had been happening behind the scenes in the US gas market.

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