Issue 32/2014 - Analytical study of three industrial hydrogen production process options

Analysis and study of three industrial hydrogen production process solutions

□ Zhang Jia, Kailuan Energy and Chemical Co.
, Ltd

Hydrogen is an important raw material, which can be used as raw material gas, reducing gas, cooling gas, shielding gas and combustion gas in industry, and has a wide range of uses
in petrochemical, metallurgy, electric power, medicine, food and other fields.
In China, most of the hydrogen used is based on the actual production situation, combined with local resources, energy and other favorable factors, the establishment of corresponding hydrogen production devices
.
However, due to the different choices of raw materials, the process route and hydrogen production method are also different
.
At present, the main domestic industrial hydrogen production methods are: water gas, semi-water gas and coke oven gas hydrogen production process using coal as raw material; hydrogen production from the conversion of natural gas and petroleum products; Chemical cracking hydrogen production process
using methanol, synthetic ammonia and other chemical products as raw materials.
According to the technical requirements of the device for hydrogen quality, each production can choose absorption, adsorption (pressure swing adsorption and temperature adsorption), membrane separation and other separation and purification technologies
.
This paper mainly discusses three typical hydrogen production schemes, including coke oven gas hydrogen production, natural gas steam conversion hydrogen production and methanol steam conversion hydrogen production process, which provides a favorable reference
for choosing the appropriate hydrogen production method for hydrogen.

First, the introduction of three hydrogen production scheme processes

1.
After the coke oven gas hydrogen production process
is decoking and naphthalene through the adsorption tower, the coke oven gas with a temperature not higher than 30 °C enters the desulfurization tower from the bottom of the tower, and enters the ammonia washing tower after contacting the desulfurization liquid sprayed on the top of the tower in reverse contact with the desulfurization tower, and enters the raw gas compressor after washing and removing ammonia by circulating ammonia water and ammonia steaming wastewater, and the raw gas compressor is a screw compressor
.
The compressed feed gas pressure is about 0.
5MPa, which directly enters the variable temperature adsorption (TSA) process
.
TSA purification device adopts the principle of variable temperature adsorption, the system adopts 2 adsorption towers (one continuous adsorption and decontamination, one to achieve regeneration), and each pretreatment tower needs to go through five steps
such as adsorption, reverse depressurization, heating, cooling and pressurization in one cycle.
After the pretreatment system removes naphthalene, tar, NH3, H2S and other aromatic compounds, the coke oven gas is compressed to about 1.
8MPa by the second and third stages of the compressor into the subsequent PSA hydrogen purification system
.
Crude hydrogen product gas containing a small amount of oxygen (about 0.
3%) is obtained from the pressure swing adsorption section, and through a catalytic reaction, oxygen and hydrogen are generated into water, and the water in the mixture is dried and removed
by variable temperature adsorption technology.
Drying adsorption adopts isobaric variable temperature adsorption, and the dew point of hydrogen after drying ≤-60 °C
.
The device boundary area and flow are shown in Figure 1
.

As can be seen from Figure 1, the coke oven gas hydrogen production device is mainly composed of
three major systems: gas purification, compression, pressure swing adsorption and hydrogen extraction.
Gas purification system includes decoking, deamination, benzene, desulfurization, TSA (variable temperature adsorption) purification; The compression system includes primary compression and secondary compression; Pressure swing adsorption hydrogen extraction system includes: PSA hydrogen extraction, deoxidation drying
.

2.
Natural gas from the boundary area of natural gas steam conversion hydrogen production process
enters the hydrogenation converter reaction after filter dust removal, gas-liquid separation and preheating, and the reacted gas is desulfurized through the desulfurization
tank.
The desulfurized natural gas is mixed with medium-pressure steam to reach a certain water-carbon ratio (3.
5~4.
5), and after catalytic conversion in the conversion furnace tube, it is cooled to 371 °C to change the process
.
The conversion gas enters the high-temperature conversion furnace, and a transformation reaction occurs in the high-temperature change catalyst, most of the carbon monoxide reacts with steam to generate CO2 and hydrogen, and the carbon monoxide content in the process gas leaving the high-temperature conversion furnace is reduced to about 2.
2% (dry basis).

In order to bring the transformation reaction closer to equilibrium, the outlet gas of the high-temperature conversion furnace is successively recovered by the high-variable waste heat boiler and the high-temperature transformer boiler feed water preheater, and enters the low-temperature conversion furnace equipped with copper catalyst at about 220~230 °C for further transformation reaction, and the carbon monoxide content is reduced to 0.
24% (dry basis) and sent to the decarburization process
.
The gas passes through four layers of packing from bottom to top in the absorption tower, and is in counter-current
contact with the hot lye flowing down from above.
The CO2 in the gas is absorbed, part of the water vapor is condensed at the same time, and finally 0.
1% CO2
remains in the gas.
The out-of-tower gas passes through a droplet separation tank to remove the entrained solution and is sent to the PSA process
.
The specific process flow is shown in Figure 2
.

3.
The material flow of methanol to hydrogen production process
of methanol vapor conversion is shown in Figure 3
。 The process includes the following steps: methanol and water enter the raw material liquid storage tank according to the ratio of 1:1.
5, enter the heat exchanger (E0101) through the metering pump to preheat, and then vaporize in the vaporization tower (T0101), enter the converter (R0101) after superheating to the reaction temperature after the heat exchanger (E0102), the H2, CO2 and unreacted methanol and water vapor generated by the conversion reaction are first cooled with the heat exchange (E0101) of the raw material liquid, and then the water and methanol are separated by condensation by the water cooler (E0103).
This part of the water and methanol can enter the raw material liquid storage tank, the gas after the water-cooled separation enters the absorption tower, separates CO2 by propylene carbonate absorption, absorbs the saturated absorption liquid into the analysis tower for depressurization analysis and then recycled, and finally enters the PSA device to further remove the residual CO2, CO and other impurities to obtain hydrogen
with certain purity requirements.

Second, the comparison of three hydrogen production schemes

1.
Production scale and adaptability comparison methanol
cracking hydrogen production is a more popular hydrogen production method in previous years, the process is relatively simple, simple to operate, easy to control, in the area of sufficient supply of methanol, and the scale of hydrogen demand is relatively small, such as hydrogen supply below 200m3/h, has strong competitiveness
.
Natural gas steam conversion hydrogen production is also a relatively traditional technology, which was often used in large-scale hydrogen supply occasions, such as hydrogen supply of
more than 5000m3/h.
In areas rich in natural gas, natural gas steam conversion to hydrogen production is the best choice
.
China is a large coal producer, coal prices are low, raw materials are abundant, so the cost of coal hydrogen production is one of the lowest among several processes, but due to the long process of coal hydrogen production and the slightly poor operating environment, it is usually suitable for medium and large-scale hydrogen production devices (greater than 1000m3/h).

For areas without natural gas resources and large plant scale, it is more appropriate to
choose coal gasification hydrogen production technology.
The usual suitable scales are shown in Table 1
.

2.
Comparison of investment and hydrogen production costs For hydrogen production plants with different processes of
1000m3/h, their one-time investment and hydrogen costs (reference values) are different
.
The hydrogen production from coke oven gas is calculated by referring to the coal price of 600 yuan / ton of coal gasification hydrogen production process, the price of natural gas is calculated at 2.
5 yuan / m3, and the price of methanol is calculated
at 2600 yuan / ton.
The investment and cost analysis of hydrogen production from different feedstocks are shown in Table 2
.

3.
Product quality analysis
From the current production of the device, natural gas steam conversion and methanol steam loading hydrogen production device produced hydrogen-rich mixture and coke oven gas, its impurities contain carbon element, after PSA pressure swing adsorption device treatment, hydrogen purity can reach more than 99.
9%, can be used
in many fields.

Table 1 Typical construction scale of different hydrogen production schemes m3/h

Process route Suitable for scale Preparation of
natural gas steam conversion hydrogen production >1000 Hydrogen production by methanol vapor conversion with refinery gas 20~2500 —coke oven gas
hydrogen production 1000~200000 —

Table 2 Investment and cost analysis of different hydrogen production processes

Process route Investment/yuan·m-3 Hydrogen cost/yuan·m-3
natural gas steam conversion hydrogen production 6620 0.
8~1.
5 methanol steam conversion hydrogen production 10000 1.
8~2.
5

coke oven gas hydrogen production 13000 0.
6~1.
2

III.
Conclusion

Through the comparative analysis of three typical hydrogen production processes, such as coke oven gas hydrogen production, natural gas steam conversion hydrogen production and methanol steam conversion hydrogen production process, it can be seen that:
(1) For production plants above 3000 m3/h, only coke oven gas hydrogen production and natural gas steam conversion hydrogen production processes
can be selected.
From the perspective of investment scale, the natural gas steam conversion hydrogen production process is relatively less investment, but it is more
affected by the source of raw materials than the coke oven gas hydrogen production process.
In areas where natural gas feedstocks are abundant, it is recommended to give priority to the natural gas steam conversion hydrogen production process
.

(2) For users of 1000 m3/h who cannot obtain cheap hydrogen-rich resources, the methanol vapor conversion hydrogen production process
can be preferred.
Regardless of the size of the plant, the price of methanol is an important factor
affecting the cost of hydrogen production.
In addition to the price of methanol, the factor affecting the cost of hydrogen production is the recovery rate
of the purification unit.
A methanol steam reformer with a hydrogen recovery rate of 72% is a self-heating unit that provides additional energy
for the plant with a recovery rate above 72%.
While the additional introduction of fuel will increase costs, it is still very advantageous
for large installations with recovery rates above 87%.