PC-JUL22-PG16-17.1_Layout 1 04/08/2022 14:38 Page 17
HEAT TRANSFER
The DPS uses recovered heat to help
pasteurise the digestate produced during the anaerobic digestion (AD) process
waste heat from chemical processing, there is no reason to waste the heat present. Perhaps the most common use of heat
regeneration is demonstrated in multi-effect evaporation systems, where a number of heat exchangers are combined, for example in the HRS DCS Digestate Concentration System. The first evaporation stage heats liquid digestate and uses a cyclone separator; the steam produced from this first cycle (usually available at 70˚C) is then used as the heating media for the second effect, whereby the process is repeated. The subsequent steam (usually available at 60˚C) is then used as the heating media for the third cycle. The number of effects is determined by the level of dry solids required and the amount of surplus heat available, up to a maximum of four cycles. After the final stage, the steam is condensed back to water and this heat is used to pre-heat the incoming product before the first stage of evaporation. In all, the heat is regenerated up to four times in the process. To determine the potential value of waste
heat, and therefore determine what it can be used for, it is necessary to know a number of
parameters about the process temperature, the product and heating (or cooling) medium being used, and the performance of the heat exchange process in terms of heat transfer area and flow rate, for example. It is therefore important to consider energy regeneration or recovery as early as possible. Heat recovery systems can be retrofitted to many processes, but their design is often a compromise. It is also important to note that not all
sources of waste heat, particularly those at low temperatures, may be suitable for heat recovery or waste heat utilisation. Online calculators are available or any reputable heat exchanger designer or manufacturer will be happy to provide advice on what is feasible. The amount of time that a process runs for will also have an effect on the viability of any project; processes which run for longer periods (such as 20 hours a day versus just a couple of hours), will be more attractive for heat regeneration. To maximise the benefits of heat
regeneration it is important that waste heat is transferred to the storage media (e.g., water or thermal transfer fluid such as glycol) as soon
as possible after its source. This is true where the waste heat is in the form of a gas, as this has a much greater energy constant than
liquid, so the heat is lost much faster. 1
The potential for recovering and using surplus heat
from industry. Final report for DECC, 2014.
https://assets.publishing.service.gov.uk/govern- ment/uploads/system/uploads/attachment_data/file/ 294900/element_energy_et_al_potential_for_recov-
ering_and_using_surplus_heat_from_industry.pdf 2
HRS Heat Exchangers
www.hrs-heatexchangers.com
https://www.frontiersin.org/articles/10.3389/fceng.2 021.679454/full
MANAGING ENERGY
EFFICIENTLY
HRS Heat Exchangers operates at the forefront of thermal technology, offering innovative and effective heat transfer products worldwide, focusing on managing energy effi ciently.
Heating Cooling
Condensing
Evaporation Waste Volume Reduction Product Recovery
HRS Heat Exchangers
info@uk.hrs-he.com +44 (0)1923 232 335
www.hrs-heatexchangers.com
JULY/AUGUST 2022 | PROCESS & CONTROL 17
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78
