How flow control principles and an innovative packing design can transform urea production

The first is commercial. Urea plants typically operate as a continuous process, without defined cycles or batch frequencies, and must adhere to this schedule to generate a profit.

The second challenge relates to the urea product itself. Urea synthesis is extremely corrosive, exposing valves to hot ammonium carbamate, which can result in corrosion rates exceeding 1,000 mm/year. To complicate matters, high velocities and substantial pressure drops are common during production, accelerating the degradation of critical components.

It’s these two customer pain points that served as the basis for our latest valve innovation, which now gives you, as urea manufacturers, a way to maximise yields by minimising the maintenance burden that currently affects product processes.

The continuous urea production process creates demanding plant conditions that require round-the-clock operation, which is the only way urea manufacturers can meet market demand.

Modern, large-scale facilities have expanded rapidly since the Bosch-Meiser process was first developed in the 1920s. This chemistry, patented and subsequently licensed, provided the world with reliable access to nitrogen fertilisers for food production. It’s also a key feedstock and a reagent for a range of industrial applications. Put simply, urea is essential to any functioning society and will be needed in increasing quantities for decades to come, driven by global population growth.

Given this steady, rising need worldwide, it’s unsurprising that many sites opt to run their assets close to the point of failure, only intervening when the risk of unplanned downtime is high.

This is evident when examining the financial impact. Based on conversations we’ve had with customers worldwide, just one day offline at a large urea plant can now cost between 1 and 2 million euros. And that lost output has to be recovered before any planned maintenance work.

Working this way is understandable, but it’s not the only option, especially now that licences for older valve technologies at many plants are nearing the end of their course. It’s a window for urea producers to strike a better balance between the business case and the realities of working with an inherently challenging medium.

Given the increasing demand across a range of global sectors for urea products, manufacturing plants are having to operate for longer periods and meet higher production targets than before. This places additional strain on legacy plant equipment, particularly the valving systems that support the production process. These valves are beginning to exhibit design and operational flaws that cause unplanned, costly shutdowns.

It’s impossible to eliminate the harmful effects of urea synthesis. However, they can be managed more effectively with proper material selection and a deeper understanding of sound-flow control principles.

Urea production is particularly challenging as clogging and solidification/crystallisation of the medium can sometimes occur when the temperature drops. Simple, single-stage valve geometries are one solution; however, these designs also make it more challenging to dissipate energy effectively. For urea production, it’s not uncommon in some processes to see pressure changes of up to 180 bar. If left unchecked, these steep pressure drops can lead to more serious problems, as flashing and cavitation are inevitable in such applications and can severely damage the valve’s interior.

Our valve incorporates a smart design of the seat and plug shapes, which provides extra protection for the sealing surfaces. The valve transitions from fully closed to regulating mode via a deadband region, where the sealing surfaces are separated, but flow has not yet been established.

This reduces the risk of erosion in critical sealing areas by directing high-velocity flow and entrained particles away from sensitive valve surfaces during low openings. During normal control operation, flow profiling ensures that high velocity remains away from sealing areas, enhancing long-term reliability and integrity.

As an additional stage in the valve’s development, our engineering team used state-of-the-art cold-gas-spraying additive manufacturing technology. This process is applied to the most exposed areas of the seat and plug to protect against erosion and corrosion, and some of the best materials, such as Zirconium, are used for protection.

Low-angle impingement is another key design principle that’s highly effective when processing corrosive media. As shown in the graphic below, the idea is to direct the medium tangentially to the sealing surface. This minimises the direct, perpendicular impact of high-velocity flows or particles on the valve’s critical parts.

Our solution is designed to be bi-directional, allowing for optimised flow and tight shutoff regardless of which side is at higher pressure. This low-angle operation, combined with high-performance, corrosion-resistant materials such as duplex and super duplex alloys (including licensed materials), provides the valve with exceptional resistance in low-oxygen environments.

Urea fluid contains erosive particulates that are often entrained upstream. Unmanaged, these will damage a valve stem and eventually lead to packing failure. In urea production, valve packing failures cause leakage of corrosive, high-pressure urea solutions, leading to rapid corrosion, safety hazards, and unplanned shutdowns. It also results in reduced process efficiency and higher maintenance costs due to frequent valve repairs.

Comparatively minor passing incidents can quickly escalate, resulting in significant accumulations of debris and other materials around a valve body. As shown in the image below, urea solution and carbamate typically escape as hot liquid or vapour, then crystallise upon cooling.

This mass presents an operational challenge, making it increasingly difficult to achieve a tight shutoff, and the resulting leaks pose a serious safety hazard to those on the plant floor.

Packing is an area where our BEU Urea Valve excels, offering two packing designs. We focus on reliable, maintenance-free operation and on sufficient pre-compression force provided by external Belleville loading springs or integral Elgiloy springs, as well as providing you with self-energised EEEasySeal™ packing for Urea. Integrated wiper rings and carbon-fibre-reinforced packing materials mitigate the damage caused by foreign particles. A combination of proper compression over time, material selection and integrated scrapers ensures the reliable service of the packing system.

View our BEU Urea+ Control Valve product page.