Перевожу технический текст по переработке аммиака. Встретилось следующее предложение: " -    Low pressure drop (at 1.8 kg/cm 2 including riser and transfer line) in the radiant tube, which was re-harped with 89mm I.D." Никак не могу по смыслу понять что же все-таки сделали с этой радиационной трубой (re-harped, выделено жирным шрифтом). Подскажите, пожалуйста, кто встречался с подобным. Во всех вариантах перевода, встречающихся на просторах интернета либо арфа, либо кому-то что-то втолковывать.

Assessment of Current Operation 

The net ammonia production for the plant was established to be at 1442 MTPD for the Base Case (Test Run).  The natural gas consumption (including power for ISBL) was calculated at 10.0 Gcal/MT (1,230 Nm 3 /MT) of ammonia for the Base Case.  

The following are the observations from the Base Case operation:

Steam-to-Carbon ratio : The current steam-to-carbon ratio is maintained at around 4.1 to provide sufficient reforming, adequate heat for the CO 2 Removal Unit and the Ammonia Refrigeration Units (ARU).  This contributes to plant steam consumption and increases pressure drop in the front-end of the plant. 

 Reformer Furnace 107 : 

- Methane slip is 12.1 mole% dry at 798°C radiant tube outlet temperature. Catalyst was replaced in 2017 but is in poor condition. 

- Low pressure drop (at 1.8 kg/cm 2 including riser and transfer line) in the radiant tube, which was re-harped with 89mm I.D.

"[0045] Figure 4 shows four passes 401 of a radiant tube assembly for an olefin cracking furnace that has a total of eight passes (octants), each pass having 24 radiant tubes that end in six harps 402, each harp having 4 tubes and a tetra fitting for single conduit to a primary transfer line exchanger (PTLE) 105.  Only one PTLE is shown in Figure 4, but it is understood that each 4‐tube harp has an associated PTLE.  An octant, as the term is used herein, is one of a plurality of (e.g., eight, but not necessarily eight) radiant tube banks making up a flow pass."