Ammonia is the basic building block of nitrogen fertilizers, one of the most widely used agricultural fertilizers in the world.

Global population roughly doubled from approximately 3 billion in the early 1960s to around 6 billion at the turn of the 21st century. Between now and 2050, population is expected to grow by another 3 billion, according to the United Nations.

Feeding such a population will involve a combination of advancements, including relying on increased plant nutrition, introducing new technologies and cultivating more marginal land. As a result, ammonia’s role in food production is likely to grow in importance.

“Demand for fertilizers, the majority of which are ammonia based is driven by the need for food, which in turn is driven by the size and wealth of the population,” says Bala Suresh, senior consultant and director of IHS Chemical.

In recent years, a number of improvements have occurred in ammonia manufacturing processes that both increased energy efficiency and reduced operating costs. These production gains are being achieved through development and implementation of better process conditions and more efficient equipment design. In the past decade, ammonia process technologies have been commercialized worldwide by major licensors such as Haldor Topsøe, Ammonia Casale, Uhde and KBR.

Ammonia Market Overview

Ammonia production in the U.S. is set to increase significantly, mainly due to the abundant availability of cheaper shale-based natural gas raw material, says Suresh. Most of the announced capacity expansion projects are connected to downstream products such as urea and ammonium nitrate. Demand from these products also helps to drive ammonia production.

Crop prices also exert an understandably big impact fertilizer demand. “Crop price, like corn to fertilizer prices, has had a steady correlation,” says Suresh. In 2014, crop prices fell and farmers cut their application of fertilizers. In general, higher crop prices encourage farmers to apply more fertilizers to increase productivity and, consequently, increase their income. Lower crop prices tend to have an opposite effect.

Ammonia demand growth may be tempered by lower biofuels production in the U.S. Environmental factors play a major role in favor of advanced biofuels, which are expected to have lower greenhouse gas emissions than corn-based conventional biofuels, says Suresh. Corn production is one of the largest consumers of ammonia-based fertilizers worldwide. In the near term, however, corn-based conventional ethanol demand is expected to remain steady until competing methods mature. Nevertheless, production of conventional biofuels based on corn is forecasted to slow after 2020. The land required for that production is also forecasted to decline, according to international estimates. This has the possibility of reducing demand for fertilizer for corn crops, impacting ammonia markets.

Most ammonia is produced using processes that rely on natural gas. (Chinese producers, by contract, rely on coal as part of the production process.) A November 2014 report from the U.S. Energy Department’s Energy Information Administration anticipated that the price of natural gas would fall to $3.80/MM Btu in 2015, down from $4.50/MM Btu in 2014. A similar downward trend was expected in Europe in contract to China and Russia, where natural gas prices were expected to increase in 2015 compared to 2014. All these factors directly influence nitrogenous fertilizer pricing. Ammonia prices were supported in 2014 by low operating rates in Ukraine, Egypt, Trinidad, Iran, and elsewhere due to gas shortages.

“New capacity is coming in 2015 which should increase supply by more than demand growth,” says Suresh. “Prices may be somewhat softer in the second half of 2015.”

In 2015, as many as 50 ammonia processing projects are expected to come on stream, according to Suresh. In the U.S., Yara and BASF are building a standalone ammonia plant in Texas that is scheduled to enter service in 2019, with an expected capacity of roughly 750,000 metric tons per year. And US Nitrogen is building an ammonia plant in Tennessee that will enter production later this year with a capacity of about 66,224 metric tons per year.

The Process

The main industrial route for the production of ammonia is the Haber-Bosch process. In this process, nitrogen and hydrogen gases react catalytically under high temperature and pressure. (Other production processes include indirect electrochemical synthesis methods and membrane reactors.)

Schematic of the Haber-Bosch process. Image source: Wikipedia In the Haber-Bosch process, nitrogen is attained from air, while hydrogen is obtained from the catalytic reforming of natural gas. Generally, ammonia from natural gas is the least energy intensive means of production. Coal, by contrast, is the most energy intensive. Approximately 72% of ammonia is produced from natural gas using a steam reforming process.

In steam reforming ammonia plants, hydrogen is made by reforming natural gas in order to produce synthesis gas consisting of a carbon monoxide and hydrogen mixture. The carbon monoxide reacts with steam in a water-gas-shift reaction to produce carbon dioxide and hydrogen. Later, carbon dioxide (CO₂) is recovered for uses such as urea production or to be vented to the atmosphere. In the last synthesis loop, ammonia is produced from the reaction between hydrogen and nitrogen.

Generally, the type of feedstock used is important as it determines which hydrogen production process will be applied. The steam reforming process uses natural gas or other light carbon fuels. The feedstocks used for the partial oxidation process are heavy oils and coal. The type of feedstock used also plays a role in the total energy used and amount of CO₂ produced. For instance, coal as feedstock for hydrogen production in ammonia plants is characterized by high energy consumption and CO₂ emissions. Hence, converting from coal or oil-based ammonia production to natural gas-based production may result in key energy and greenhouse gas emission savings.

Improved Design

The latest converter configuration from Haldor Topsøe in the radial flow technology is based on the principle of utilizing small catalyst particles on a volumetric basis to provide better conversion than larger size particles, according to Hans Christian Ferdinandsen, proposal manager at Haldor Topsøe. In general, ammonia synthesis converters differ according to type of flow: axial, radial, or cross.

“Radial flow pattern results in a significantly lower pressure drop across the converter than the axial flow design,” says Ferdinandsen. This makes ammonia production more energy efficient and more profitable.

KBR's advanced ammonia synthesis converter also utilizes the radial flow technology, where all of the catalyst beds are in radial flow for low pressure drop, and intercoolers are situated among the catalyst beds for maximum conversion and heat recovery. Uhde’s Three Bed Ammonia converter also follows the radial-flow principle to help ensure energy efficiency.

In general, most ammonia licensors follow the radial flow concept to achieve goals that include a low-pressure drop in the synthesis loop, large catalyst volume and optimum usage of reaction heat to generate high-pressure steam.

The ammonia process plant consists of several sections: sulfur removal (desulphurization), steam-methane catalytic reformer (primary and secondary reforming), shift conversion, carbon dioxide removal, methanation, ammonia synthesis and product recovery.

Aside from the ammonia converter, the tubular reformer known as the primary reformer is similarly critical as it also affects the performance and cost of an ammonia plant.

“The reforming unit is a crucial part where heat is transferred to the process in a radiant section of a furnace chamber,” says Ferdinandsen. “The challenge here is the efficient transfer of the heat under safe conditions.”

The Haldor Topsøe tubular reformer design sought to solve this challenge by manipulating certain parameters, such as flame direction of the burner design to eliminate flame impingement on the tubes to ensure tube integrity and burner configuration, in which burners are positioned in several horizontal rows along the vertical tubes.

To tackle a similar challenge, Uhde designed a primary reformer furnace to incorporate top firing to ensure a uniform tube temperature profile. Each tube row is connected to a separate outlet manifold, while having an internally-insulated cold outlet manifold system and an internally-insulated reformer tube-to-manifold connection. On the other hand, KBR introduced a reforming exchanger system to replace the primary and secondary reformers with a fired pre-heater, an autothermal reformer, and reforming exchanger. This design avoids direct firing on the exchanger tubes that in return removes hot spots and allows for process temperatures to be lower.

Recently, new ammonia plants tend to be larger with improved economics of scale. However, the well proven capacity of 2200 MT per day is becoming the preferred capacity according to Ferdinandsen. He says that, in general, the advantages of higher capacity are not always preferred by all producers as the larger equipment may result in fewer suppliers and thereby leaving the producer with less flexibility than many prefer.

Catalysts

The magnetite catalyst possesses two characteristics that are favorable for industrial application, according to Ferdinandsen. He says “the cost is lower than that of any alternatives and it has a low deactivation rate leading to long operational time per catalyst charge.”

A magnetite catalyst by Haldor Topsøe, says Ferdinandsen, is an example of how new catalysts can be developed despite not being one of the most thoroughly investigated catalysts in the ammonia industry. Magnetite catalysts deliver considerably higher activity in lower converter beds, while retaining exceptional thermal and mechanical stability. Both Uhde and KBR use magnetite-based catalysts for their ammonia synthesis converters.

Advancements in the ammonia industry and its catalyst technology will never stop as the catalyst of any advancement can lead to enhanced thermodynamic efficiency and lower product prices.