Enhancing Safety of Ammonia/Urea Fertilizer Complexes
Sunny Choi, Sandeep Chaurasia, Sachin Gupta, Akshat Khirwal
IRESC
Abstract
Fertiliser is an essential component in maximising crop yields in the agriculture industry. Fertilizers are substances which are used to increase crop yields and crop quality by providing one or more of the essential plant nutrients nitrogen (N), phosphorus (P) and potassium (K). These three are primary nutrients and their most common sources are ammonium nitrate, urea, calcium ammonium nitrate and ammonium sulphate (for nitrogen). Based on recent statistics, about 30 to 50% of crop yields are attributed to natural or synthetic commercial fertilizer. Additionally, the fertilizer demand forecast to increase by at least 20% within the next 5 years, and the world production capacity of urea, being the preferred form of Nitrogen based fertilizer products, is expected to be more than 230 million tonnes by 2017. Ammonia is a basic constituent of most of the fertilisers (e.g. Urea, Diammonium Phosphate DAP, Ammonium Nitrate etc.) produced worldwide.

Ammonia/Urea Complexes handle materials that present both flammable and toxic hazards. Flammable hazards (fires/ explosions) are mainly associated with natural gas or naphtha handled in the frontend of ammonia plant. The presence of ammonia in the other parts of the complex is more of a concern since the toxic hazard of ammonia has the potential to cause significant off site impact..

Over the period, Ammonia demand has increased significantly and to meet the consumer demand, capacity of Ammonia/Urea complex has increased which has in turn resulted in increased inventory of hazardous material stored onsite. This eventually increases the inherent risk from these facilities. Though technology for large scale Ammonia/Urea production has been long established and successfully implemented and operated at a global level over the decades, but the technical design has not undergone any significant modifications / updates especially in terms of the safety design of these facilities compared to gas processing, refinery, petrochemical and LNG facilities. There is also a growing awareness amongst local authorities and general public towards process safety, in the light of some major accidents in process facilities worldwide, particularly in those industrial establishments which are in close proximity to populated areas. In this context, in the author’s opinion, the Ammonia/Urea production facilities also deserve a second look in order to enhance the safety design taking note of the best practices adopted in other process industries..

This paper highlights some failure cases and areas for improvement in Ammonia/Urea Complexes based on the author’s experience with risk assessments for similar facilities and supplemented by a review of historical incidents. This paper also presents some relevant safety concepts derived from general best practices adopted within other process industries, which, if implemented would enhance the overall safety of Ammonia/Urea Complexes. The safety improvement measures identified for Ammonia/Urea Complexes include the enhancement of Safety Instrumented Systems and permissive functions for furnace; minimization of bottom penetrations for process vessels handling ammonia, provision of double/ full containment tank for ammonia storage, improvement in process section and equipment isolation through ESDVs, improvement of the reliability of emergency venting system, and implementation of better emergency preparedness measures.

In author’s opinion, the safety measures proposed in this paper should be able to effectively enhance the safety levels in Ammonia/Urea Complexes and safeguard the interests of the operating companies, local authorities and more importantly the safety of general public. The paper also aims to promote discussion in the industry amongst operators and designers/ contractors towards enhancing the design safety of Ammonia/Urea Complexes.

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