**4. Industrial Tests**

The validation of the developed mathematical model is checked using the results of industrial tests of prototype WPHE installed in high-pressure column operating at an ammonia production unit. The column structure is presented in Figure 7. The reactor catalyser box (3) with connected WPHE (1) is placed inside the shell (4) which diameter is 800 mm. The shell is designed for a temperature up to 525 ◦C to accommodate working pressure up to 32 MPa. The incoming syngas is fed from the top and flowing down inside the annular gap between the shell and equipment inside it reaching inlet of WPHE at temperature t21. In WPHE syngas is heated to temperature t25 by the stream of gas after the reactor. Syngas leaving the WPHE is mixing with bypass gas that is supplied at the column bottom having temperature tb1. It is going through special channels at the WPHE sides. It is coming next by the central pipe (5) to the top of the catalyser box (3) and then into internal (9) and external (7) field tubes. It is heated there and after coming directly to contact with catalyser (8). Leaving catalyser zone (6) through a header (2), a gas of temperature t11 is supplied to WPHE for cooling down to temperature t19 and going out from the bottom of the column.

The main parameters of tested WPHE are presented in Table 2. The flow of streams in it arranged, as shown in Figure 6b with eight passes on the hot side and four passes on the cold side. The measurements of temperatures of streams coming in and out of the WPHE were performed with chromel–alumel thermocouples. For the entering of thermocouples into a column, the special high-pressure nozzle was installed. The flowrates of supplied syngas and bypass were measured by orifice flow meters. High-pressure gauges are used for measurement of gas pressures at its entrance and exit from the column.

The data of the four tests are given in Table 3. There are also presented results of modelling of WPHE performance. The experimental values of heat transfer effectiveness are calculated by Equation (8). These values are in good agreement with calculated using Equations (13), (15) and (18) of the developed mathematical model. The accuracy of the developed mathematical model can be

considered as sufficient for practical applications. It can be used for the design of this type of WPHEs. The calculation of pressure drop in WPHE is performed using Equation (12), and results are also presented in Table 3. The total pressure drop on both streams is not exceeding 100 kPa, within the limits of technical requirements; however, to compare it with test data accurately is not possible, as measured results include all the ways in which gases pass through the column, including the catalyser zone that takes the biggest part of total pressure losses. The comparison with data obtained before with the tubular heat exchanger has not revealed any differences in pressure losses.

**Figure 7.** The schematic structure of the column for ammonia synthesis: 1—WPHE; 2—header; 3—catalyser box; 4—high pressure shell; 5—central pipe; 6—catalyser zone; 7—external field tubes; 8—catalyser; 9—internal field tubes; 10—upper cover.





Before the column renovation, a tubular heat exchanger with a length of 3 m, heat transfer area of 148 m2 and weight of 2992 kg was installed. The weight of WPHE is 1694 kg, occupying a volume of 0.96 m3, that compared to tubular, is only 0.48 m3 smaller. In the remaining spare volume, an additional catalyser was added with proper modernisation of a catalyser box. It leads to a 15% increase in ammonia output.

The heat transfer effectiveness, ε*T*, is reduced compared to its value for a pure countercurrent flow arrangement from 14.6% to 17.2%. This reduction in effectiveness is caused by the asymmetrical arrangement of passes. The conclusion is that, with the crossflow in individual passes, the symmetric arrangement of passes in WPHE is preferable. The detailed analysis of this problem is made with an optimisation approach to WPHE design presented in the next sections.
