Gas conversion process Assessment 2022

ME508_Assesment3_v2_Abhijit Maitra_03Oct2019
Solution 1: Gas conversion process
a) The given system for gas conversion process (figure 1) consists of valves, controllers,
feed pumps, logic solver, gas tank, air tank, heating element, sensors, catalyst gauze
and a processing tank. In this system the usage of advanced safety instrumented
systems (SIS) and SIF will protect the plant from leakage and any accidental hazards
that could occur. This standard safety instrumented systems are required to provide
guidance to the operator to stop the possible hazard or an incident from occurrence. It
helps in the identification of the affects after utilization and its reliability, as
probability of failure on demand (PFD), Spurious Trip Rate (STR), sensitivity of the
structure and any suspicion in model [1]. While selecting for BPCS & SIS, factors to
be considered are:
 To adhere the policies and standards of safety, to check design, installation,
operational and maintenance of BPCS and SIS both.
 Acceptance of international and national regulations and performing good
practice.
 To demonstrate the docility linked by Functional Safety Management in
accordance with IEC61508 Part 1 Clause 6 and IEC61511 Part 1 Clause 5.1
[2].
 To check the competence level of the person to which the duty is assigned.
Figure 1: P&ID diagram of Gas conversion process

b) The feed gas valve opens and closes according to the pressure generated in the valve
and the timings set for operation in the control calve. The functional requirements of
the safety instrumented system can be presumed by identification of SIFs and analysis
of risk; identifying basic design parameters, HAZID, HAZOP, standard legislation
along with drawings of the design and implementation of qualitative and quantitative
risk assessment technique LOPA which delivers the necessary SIL to sustain certain
risk with independent layers of protection. In case of rise in temperature of the system
the control valve and the installed safety functions starts regulation the pressure to
reduce the temperature of the system. The HAZOP study was carried out at the time
of evaluation of safety systems to check for failsafe conditions. The economic
analysis can be done to get maintain effective cash flow; figure 2 [3].

Figure 2: Economic analysis of the system
The elements; air and gas are controlled by two different sensors and actuators with
the help of logic solver. The SRCF elements used for the formulation of a safety
related control function (SRCF) includes three data attributes:
 After the breach of the limits of the safety functions, a Triggering event is
initiated.
 To gain a safe state by the utilisation of Safety-related reaction.
 To acknowledge and asses dangerous parts of the machine which were
identified during the HAZID and risk analysis process.
In the case of failure of sensors which can happen in the case of overheating of the
system, blast in any gas chamber or air chamber due to excessive rise in
temperature or pressure and mishandling by the work handler, an immediate
action is needed to be taken to stop any risk of complete system failure. The
general philosophy for developing an SRS could be taken from clause 10.2 of
ISA/IEC 61511 [4]. The requirements for the safety should be derived by the
allocated SIF and those factors which are recognised during the hazard and risk