**3. Fertilizer (ammonia/urea) manufacturing using CO2**

Manufacturing fertilizers (ammonia/urea) is one of the ways of increasing added value of the natural gas and CO2 . The fertilizers in modern society are inevitable for enhancing agricultural productivity. The main elements used for plant growth are nitrogen, phosphorus, potash, and sulfur. Among them, the nitrogen is the most consumed fertilizer and is easily produced by using nitrogenous in air and natural gas. Phosphorus and potash are provided from minerals, and sulfur is produced as byproducts in refineries and gas plant. Ammonia containing nitrogen is a toxic gas at room temperature and cannot be used directly as fertilizer. Therefore, ammonia should be converted into other chemicals such as urea, diammonium phosphate (DAP) and ammonium nitrate, which are suitable for plant applications. Urea is produced by combining ammonia and carbon dioxide generated from production of ammonia. It is a solid, and it can be granule or prill form. The 80% of ammonia used worldwide as fertilizer is converted into urea. The present chapter deals with manufacturing and selling the urea in granule form by producing ammonia with natural gas.

#### **3.1. Production process and characteristics of facilities**

The production process consists of following facilities, and its overall block diagram is represented in **Figure 5**.


**Figure 5.** Block diagram of ammonia/urea plant.

#### **3.2. Ammonia plant**

**3. Fertilizer (ammonia/urea) manufacturing using CO2**

selling the urea in granule form by producing ammonia with natural gas.

**3.1. Production process and characteristics of facilities**

the natural gas and CO2

200 Recent Advances in Carbon Capture and Storage

sented in **Figure 5**. - Ammonia plant



**Figure 5.** Block diagram of ammonia/urea plant.



Manufacturing fertilizers (ammonia/urea) is one of the ways of increasing added value of

cultural productivity. The main elements used for plant growth are nitrogen, phosphorus, potash, and sulfur. Among them, the nitrogen is the most consumed fertilizer and is easily produced by using nitrogenous in air and natural gas. Phosphorus and potash are provided from minerals, and sulfur is produced as byproducts in refineries and gas plant. Ammonia containing nitrogen is a toxic gas at room temperature and cannot be used directly as fertilizer. Therefore, ammonia should be converted into other chemicals such as urea, diammonium phosphate (DAP) and ammonium nitrate, which are suitable for plant applications. Urea is produced by combining ammonia and carbon dioxide generated from production of ammonia. It is a solid, and it can be granule or prill form. The 80% of ammonia used worldwide as fertilizer is converted into urea. The present chapter deals with manufacturing and

The production process consists of following facilities, and its overall block diagram is repre-

. The fertilizers in modern society are inevitable for enhancing agri-

**Figure 5** shows the block diagram of ammonia/urea plant. This plant manufactures ammonia by use of natural gas and air. The ammonia and carbon dioxide (CO2 ) generated as byproduct are used as raw materials for manufacturing urea. For enhancing operational flexibility and the possibility of direct sale of ammonia to customers, the ammonia storage tank is required. Block diagram of ammonia plant is shown in **Figure 6**.

**Figure 6.** Block diagram of ammonia plant.

The existence of sulfur substances in gas reduces the activity of catalyst. For this prevention, the sulfur substances shall be removed from the gas. And then the produced gas is supplied to reformer. The synthetic gas is generated in passing through various reaction steps of the reformer. In reaction steps, the air is supplied for providing nitrogen needed in producing ammonia. After these reactions, the main substances of hydrogen (H2 ), carbon dioxide (CO2 ), and nitrogen (N2 ) are produced.

The produced CO2 is separated by using amine in CO2 removal unit and then sent to urea plant. The CO2 and CO that are not eliminated in the CO2 removal unit are removed in methanation unit. N2 and H2 are reacted in ammonia reactor, and then the ammonia (NH3 ) is finally produced.

#### **3.3. Urea plant**

Ammonia (NH3 ) and carbon dioxide (CO2 ) produced from ammonia plant reacts as below, and the urea and water are produced.

$$2\,\text{NH}\_3 + \text{CO}\_2 = \text{H}\_2\,\text{NCONH}\_2 + \text{H}\_2\,\text{O} \tag{9}$$

The intermediate products such as carbamate, nonreacted ammonia, and CO2 are separated and recycled as raw materials. The water generated as byproduct is removed during the step of condensing urea. **Figure 7** shows the block diagram of urea plant.

The produced urea liquid in high temperature is solidified by cooling. The urea is solid state in atmospheric conditions, and it can be a form of prill or granule. The size of prill is smaller than granule. The investment cost for granulation processing is higher than that of prilling, but the granulated urea is more suitable as fertilizer. The granulated urea is packed in various sizes of bags for storage in warehouse.

For the operation of above plants, the following utility & offsite facilities are required:



**Figure 7.** Block diagram of urea plant.
